The DSP used in the empeg is the SAA7705H, a complex chip specifically designed for car audio applications. The chip is now `not promoted'.
Philips publish a data sheet (preliminary specification) and a user manual (NBA/AN9801) for this part. The data sheet also mentions the EPICS6 Programmers Guide, but Philips don't supply this as it this is only required if you want to write your own DSP ROM code.
The external tuner unit sold (but now sold out) for the empeg Mark II contained the Temic 7660 tuner module.