@ Karlos
Can't really help you on low-level specs, but there's some interesting development material available.
This fine file from the Wayback Machine includes something called A56, an assembler for the DSP.
This old page has some more details about the Delfina.
Most of Petsoff's site seems to be very adequately archived, so you should be able to access most of their stuff.
If you do start developing for the Delfina, I think many users (like me :-)) would be very grateful. There's some good stuff on Aminet that could stand to be updated, and it would be the Event of the Year if you could finally crush all the bugs in delfina.library
EDIT: I've also got all those floppies shown in the picture in that second link, but I don't have access to them right now. I'll search through them next time I do for anything missing from the Internet Archive.