We just did an audio upgrade to a 2005 X5 with Nav and Cassette and "DSP".

It had dealer-installed Sirius.

The menu read "DSP" on the Nav screen, but the changer had no Digital Coaxial Cable. Apparenlty there is a higher-end system than this which does have this missing digital coaxial cable. Perhaps that's the variable here? There seem to be two levels of DSP - the one above being a "quasi" DSP...