Here is some good info:
https://www.zpost.com/forums/showthr...highlight=grom
Mine is a 2006 Z4M Roadster w DSP headunit and 10 speakers. It is the least upgradeable stereo option to come with these cars.
I had a shop do the install, I think it was $150, including running a cable to my mount. I bought a pro-clip custom mount, I've been using them for a long time and like their products.
Cheers,
Eamonn aka eggman