I just asked Philips about this.

The document they don't distribute is the EPICS6 Programmers Guide,
but that is only required if you want to write your own DSP ROM code.
If you use the standard part, which I presume the empeg does, it comes
with DSP code which is documented in the user manual (NBA/AN9801).

Philips supply this manual free of charge. They sent it to me as a
pdf, marked UNCLASSIFIED and with no copyright markings or distribution
restrictions, so I feel confident I can put it here:
http://empeg.org.uk/info/saa7705h-man.pdf

Now, what can we do with it?