Geia sou Spyro,
I guess you have already tried all the obvious stuff, it's a mystery why these cards dont work...
My 3000 worked fine with superbuster 7 and a Picasso II and an X-surf II. I have since upgraded to buster 11, but that would only be required if there was any DMA board installed.
Have you tried messing with any jumpers on the mobo?
Anyway, sorry I cant really help, but if you need a fellow A3000D Greek owner to test/discuss, let me know (i'll be hanging around #amigahellas too).