started a new thread that has to do with this somewhat
Check here for some interesting info from alpine:
http://www.msprotege.com/forum/showthread.php?p=1161347#post1161347
Though I do not have a Mazda 3, I do have a Mazda Tribute which led me here while I was researching ways to get auxiliary inputs working on my factory HU.
I first found the PIE electronics interface mentioned also in the sticky:
http://shop.store.yahoo.com/logjam/piemazpcalp.html
Then I also...