Originally Posted by Keto
Easy. They wanted to have that low, low base price.
On my E46 I did a DIY and replaced my speakers, amp and added a 12" subwoofer. That was a hella day of work. Parts cost me ~$800, all ebayed, mostly a/d/s. It sounded great until the amp died (I didn't mount it with enough ventilation, it was in the trunk below the trunk floor). I had one of the "better" local shops put a new amp in. I had to teach them how to adjust the gains to avoid hissing and I still have a slight ground loop. I'm afraid to drill a new hole to ground it and fix it.
If you live near a good audio shop, bless you, but I'm screwed. Oh, and my speakers "fit" but now the doors squeak ever so slightly because they're clipped a bit off tolerance according to my dealer.
Moral of the story -- aftermarket is only good with qualified people. I'm not one, and it seems that no one else in New Orleans is either.
I envy people who live near a shop that knows what they are doing.
I have a somewhat similar upgrade story with my old 300ZX. I bought everything from Crutchfield, and installed it myself. It was kick ass by the time I was done, but it did take me two days. Fortunately it never stopped working, and I didn't damage anything, but the car was already 7 years old so I didn't care. I would care with a new M3, so you are right; it should be done professionally. The question is can you beat a $1900 upgrade with say a $1200 job (including labor)? I don't know. I'd have to do the research. Actually, I just want to live with the base system to see how I like it first before I do anything.