'04 Nav headunit to '03 business headunit issue w/ Grom iPhone kit

[ChrisPiascik]

I'm hoping someone can help me with some Factory headunit issues on my '04 3.0i...

My car came with premium audio and Nav. It has subwoofers behind the seat, amp next to the battery, it had a Bluetooth box, the Nav dvd thing. From everything I've read, this is the DSP audio. I bought the Grom audio kit to hook up my iPhone and purchased the DSP adapter.

When hooking it up the regular grom kit hooked up without the DSP adapter and worked without any issues. I couldn't find any coax cable for the adapter to even plug into and since it worked perfectly without it I didn't look further.

My Nav screen was not working properly when I got the car. It was stuck open, rattled a bit and there was no backlighting so you could barely see it. I decided to remove it all together and It's been like that for a couple months now. I really only use my iPhone to listen to things in the car so the lack of screen on my Nav-based headunit hasn't been a big deal. After resetting my battery recently I noticed the sound settings went back to their defaults and I can't fix them without a screen. That was a bit annoying.

I ended up finding a Z4 business headunit from an '03 that supposedly had premium audio so I bought it hoping it was the answer to all my problems. When it arrived I hooked it up and everything seemed great, the radio immediately worked. The subwoofers were working so I assumed it was utilizing the premium audio. BUT, when I hooked up my iPhone it got power as usual and it even showed the artist/song info on the headunit display but I could not get the sound to work. I triple checked everything on the iPhone end and even tried it in my other car to rule out anything that wasn't the Z4 stereo. Does anyone have any idea what's happen? On a side note I tried to test the CD player and I couldn't get that to work either. When I put a disc in it tries to read it and then says "error". I'm assumed that's just a dirty laser or something. But in reality I'll never use it anyway.