I found the Mazda6Club forum, but back when the car came out everyone was wondering the same thing and nobody had an answer. I tried an FM transmitter, but it was horrible. I upgraded to an FM modulator, which seemed to work okay. It was similar to an FM transmitter, except it gets plugged into the car power and directly into the antenna of the radio. It didn’t have any static (at first), but was kind of muddy and dead sounding. I didn’t really use it much until recently, and now when I went to use it I’d get about 10 minutes of muddy sound, and then it would start getting static. I bought the modulator used, so I imagine it was just on the fritz.
So, I went back to the forums, and, lo and behold, there was a solution! The Sylfex AuxMod Basic plugs into the factory radio, and emulates the optional tape deck. I installed this yesterday and, shebang, awesome direct plugged in sound. They are also making an AuxMod advanced, which will emulate the optional MD player – this will have the added ability to send signals to a computer or ipod to pass on the radio/steering wheel controls do the remote player. Since all of Mazda’s audio gear now shares components, this device will work on most newer Mazda’s. Getting this device was a lot cheaper than the alternative (replacing the car for one that has an audio input).
Installation was very easy, especially with my 2 year old son helping. He sat in the driver’s seat and made sure that all the buttons and dials everywhere within reach could all be turned, switched, etc. Here are the guides I used: