This article is from the Apple II Csa2 FAQ, by Jeff Hurlburt with numerous contributions by others.
First, if your RamFAST is the Rev. C (full-length) card, it cannot DMA to 8MB; so, you will have to turn DMA off. The Rev. D can DMA to 8MB fine. Second, make sure there are 8 SIMMs on the Sirius. Alltech used to say that you are supposed to take out one of the SIMMs when using the 8MB Sirius card on a ROM 3; but, this leads to problems. Plug in all 8 SIMMs and use it that way. You lose the 1MB from the motherboard this way, but you gain it back on the 'extra' SIMM you put in. By: Supertimer