I run IIci and IIcx systems loaded with Nubus cards and accelerators with no problems on the old stock supplies. You said it freezes (maybe checking the cache module) but doesn't stay that way so the card works? What Mac OS version are you running and is the PRAM battery good? I think the system stores which CPU to boot from and cache settings in PRAM and that might affect the system booting if the battery is dead or dying.