wow, I went away on vacation and there's a whole bunch of stuff I need to catch up on:
so here's the other twist: I brought this up to my buddy who's a Porsche technician.
Now, this isn't a Porsche, however, he told me that many of the new cars, when looking at diagnostic codes, the signals go through the radio. If you put an aftermarket system on, the diagnostics go to the radio, don't recognize it, and stop there. This way, the technicians can't read the codes.
He didn't know if this was the case with Mazdas.

Anyone know, definitively if replacing the stock stereo will interfere with this? I could ask my dealer, but I think I'd just get that puzzled look