You only alternative is to buy an aftermarket Headunit. He was correct about it not working, to a certain degree. It will work, but you will more than likely have to bypass the factory amp. another issue you may encounter is the fact that most aftermarkets are 4ch, and your car has between 8-12 speakers, hence the splitter comment.
So, it can be done, and it would cost less than $550, but you wont retain factory controls.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>