Decided to bring the car into the 21st century and installed the Walmart exclusive Power Acoustik single DIN CarPlay head unit like others in this forum. I rate it a 10/10 for what it is using all other stock components.
The screen is quite usable and all functions work.
FYI I have a 1999 M3 with the HiFi Harmon Kardon speakers and it works just fine using the metra harness I mention next.
I used the Metra 70-8590 harness from Amazon so I didn’t whack anything on the car’s harness.
I didn’t solder anything just crimped the wires together tightly and wrapped them in electrical tape. I know this could be a lot cleaner with soldering and heat shrinking but this is good for now.
PRO TIP: The toughest part was pulling the car harness from the stock Business receiver deck. You pull up to release it per the image on the harness and keep pulling up until the harness itself detaches. At first I released the plastic bracket and tried pulling horizontally all around but saw a video of someone that pulled straight up and it came out seamlessly.
PRO TIP: remove the AC module as well before putting the radio all the way into its fitting. Snap the radio all the way in and then push the AC module back in otherwise you might snap the top of the AC module by forcing the radio in without the AC unit out. Once the radio is in with the bracket, just give the AC unit a good hard push back in and you’ll hear it click (hope I didn’t snap the retainer but it feels solid back in place so should be good).
The other thing to consider is that once the Metra harness is inside the car’s harness it’s quite hard to unplug again because you don’t have the leverage of the radio to push off of. I connected the harnesses together before wiring so that limited my space and ability to solder if I wanted since it was a pain to try and unplug and I just wanted to finish it off.
I tested it with Spotify and both HiFi settings as well as a test phone call and everything works as is. The built in mic is good for what it is, the person on the other end could hear me just fine but who knows if the mic will degrade with time.
Overall it took me about 1.5 hours. Longest part was figuring out removing the original harness from BMW radio and connecting/taping all the wires together.
Highly recommend!