Thanks to the Internet and this forum I was able to complete a total Bose-ectomey. At the request of several forum members I decided to put together the path that I took. This is not the only way to accomplish this task, just the method that I used. I take no responibility for what others may or may not do to their cars. Unless you are comfortable with soldering and making 100% accurate wiring changes, I would leave this to a professional. I will put here links to the threads and locations where all the data I used are located and give full credit to the original posters for their insight and help.
FYI – I have an 04 MSM that had the silver double DIN Bose radio. I elected to go the single DIN route since at some point I may want to put gauges in above the radio. Any deck less than 6 ˝ inches deep will fit in case you opt for something else like a double DIN setup.
Here is what I purchased to start the project:
Kenwood KDC-X996 single DIN radio (Amazon)
A pair of Pyle 8” 3 way speakers (Amazon) for the door speaker replacements
A radio mounting kit (Metra 99-7505) Crutchfield (I ended up only using a couple of pieces.
Wiring harness adapter (Crutchfield 120 70-7904)
Single DIN Pocket (Metra 88-00-9000)
http://www.parts-express.com PN# 265-671
A set of XTC 8” round foam baffles
http://www.parts-express.com PN# 260-792 These were difficult to find anyplace else.
1. First step of course is to disconnect the battery to avoid letting the smoke out of any of the critical components.
2. For removal of the old (DEAD) stock Bose head unit I cut an old wire coat hanger and made my own removal tools. For the double DIN I made a total of 4 since there are four holes on each side that need to be released. Great information from Aaron Lopez at
http://www.miata.net/garage/miata_radio_removal.html It is all a lot easier with the shift knob removed.
3. Unplug the big multi-wire connector. There is a release lever. Also remove the antenna connection. My radio did not have a ground wire.
4. Set the old radio aside as you will need that alignment rubber piece from the back of it later.
5. Also remove the rear windblocker by taking off the center panel and unplugging the feed to the little amplifier there. This way later your new radio will not be sending any signals to that amp and possibly causing harm to your new radio.
6. Wire the wiring adapter and the Kenwood wiring together. I chose to solder each one together and heat shrink each individual wire. My source for this information was
http://miata.fosketts.net/index.php?title=J-01 
7. After setting the completed wiring adapter aside I turned my attention to jumpering around the front Bose amps that are buried under the dash over the transmission tunnel. It would require removing the dash to totally remove these little amps. I elected to leave them in place and leave them disconnected. With the radio removed you can see the connector way down close to the throttle peddle. Getting to this plug is a real PITA. Getting its latch to remove was the hardest part. Great info at
http://miata.fosketts.net/index.php?title=Bose_Amp After getting it unplugged I was able to pull it upwards into the radio hole and work on installing the bypass jumpers that way. I used 4 short pieces of wire that were large enough to provide a tight fit into the female connection on that plug block. I solder/tinned the wires and then cut the wire end to a length so that when plugged in, only the insulation was showing. This will take 4 wires total.
8. At this point I removed the door interior panels in preparation for replacing speakers. I found a good description with pictures at
http://www.mazda-speed.com/forum2/index.php/topic,26820.msg288802.html#msg288802 The passenger door only has one wire to disconnect and that is the one to the tweeter speaker. This disconnects right up next to the tweeter. The driver’s door has two wire sets, the tweeter like the passenger door and the wires to the lock switch. There are some U shaped brackets that pulled away in this process leaving the round snap-ins still on the door. I used epoxy to remount them onto the door panels and set them aside to dry.
9. After removing the 4 screws holding the 8 inch speaker in & unplugging the connector, I did a test fit of my new speaker and found that they were a tad lager but the mounting holes lined up right. I used the wires that came with the speakers to make up a pigtail about 6-8” long and soldered on a couple of spade connectors that would plug into the existing plug that came off the old Bose speakers. Keep in mind that the green & Yellow wire is + and the green wire is -.
10. I punched a small hole in the foam baffle at the bottom and fed the wires up into the center of the baffle. With the baffle in place (untrimmed) I plugged the wires onto the speakers and screwed the speakers in using the original 4 screws. I then trimmed off the excess foam. I left the door panels off till everything was all powered up and tested later.
11. The old Bose 8” speakers were 0.5 ohm & totally not usable. The door tweeters on the other hand were 4 ohm and match the new Pyle speakers I installed. I was surprised at how light the Bose speakers were as compared to the Pyle’s.
12. Now to install the new deck.
13. I used the little plastic parts of the Metra install kit for the side latches. I had to cut them a bit since they seemed more for a double DIN setup. I used the countersunk screws that came with the Metra kit. After test fitting it I decided that a rear support was necessary, just like what the original speaker had. I removed this off the old radio and had to make a new screw that would fit the tapped hole that was already there on the back of the Kenwood. The old post in the middle of the rubber part was not compatible so I found a bushing and the proper sized screw to make it all work. Without this post, the radio had no support at the backend. With as much road vibration our cars generate everything needs to be pretty snug and secured.
14. I used the Kenwood face surround that came on the radio. It fit OK but had to much slop to the sides and as a result the side catches would not hold the radio in as securely as I liked. To that end I had a bit of Black ABS plastic which was3/32” thick and cut out a couple of little strips and glued then on the sides of the Kenwood surround using some super-glue.
15. With the modified face surround back on the radio and the faceplate removed, it was time to connect the main wiring adapter into the car wiring harness and then into the new radio, making sure that both plugs went in all the way and snapped. This process can be a bit of a juggling. An extra set of hands would help.
16. The antenna connection is pretty straight forward.
17. There are two more wires to connect. One is the USB for the iPod. This one I ran down to the right and eventually had it end up inside the glove-box. The other is the wire for the hands-free microphone which I mounted just above the steering wheel close to the instrument panel. The wires was extra long but after removing the panel below the steering column I found a place to wire-tie the extra together and up out of the way.
18. As I slid the radio up in place and made sure the rear rubber guide was lined up and that all cables were not being pinched, I heard it snap into place. PERFECT! You will note in the picture below how the two added plastic pieces snugged everything up.
19. Once the radio is in, I put the faceplate on and reconnected the battery so I could test it all and validate that the door speakers and the deck were functional. What a rush to have it all work 100% at first try!
20. With assurance that the door speakers and the radio were OK then it is time to put the door panels back on and start to finish up the dash installations by adding the cubby. I suppose at this point you could pursue using the empty DIN slot above the radio for gauges if desired. I chose to add the cubby at this time. It also required a couple of plastic shims on the side of it as well. I used the largest of the surrounds face plates that came with the Metra kit. I was warned via the forum that the side screws are to easily overtightened.
21. Once you snap the cubby in, it is time to put the shift knob back on and then turn your attention to the windbreaker behind the seats.
22. The two windbreaker speakers can be used as-is since they are also 4 ohm speakers. There is only room for 2” speakers there and the stock ones appear to be identical to the tweeters in the doors. These speakers have capacitors just like the door tweeters. These capacitors act as a high-pass filter that blocks the low frequency sound and only allows the higher frequencies to pass.
23. I elected to take the whole thing apart and replace them both with a couple of healthier mid-range speakers. I go mine by salvaging a couple out of a Macintosh computer. Better ones are available from a variety of sources. I also did not install any high-pass capacitors.
24. I did remove the little amp in the wind-blocker and wired the speaker wires directly. I cut off the terminal block that plugged into the Bose amp. The orange & black were cut since I had no need for power at that location. I suppose that you could use this power for some other low poser accessory. No sure how much power is in that circuit.
25. Reinstall the wind-blocker and it is all done! Nothing to do now but read the manual and enjoy all the new features of the new deck.
