what do u mean with SGI ?? sorry never seen this b4 (I think! ???)
I Use RME Multiface (1 adat I/O).. but the slightly cheaper Digiface has 3 ADAT I/Os..
don't know if this will do 4 ya.. but it should b in the 800 $ range (or cheaper including the interface with the pc, either pci OU pcmcia).
Hope this Helps,
Z