CD Changer for 2001 525I

[Flyboy]

Bought a used 2001 525I. It has cassette in dash WITH DSP and I want to install a CD Changer in trunk mount area. There are two wires, one is a 3 pin (power?) and a small coaxial (DSP?) that I am told are used to connect to the changer.

I am also told very few changers work with the DSP stereo and you either need a $150 connector to run aftermarket such as Alpine..or...plunk down $600 for a BMW changer at the dealership.

Any truth to these rumors because I see alot of DSP capable units on EBAY and would rather pay $300 versus $600?

Thanks