According to Dave Haynie, the rev 9 is flawed and is likely to cause trouble (from BBoAH):
The Level II part (about twice as many gates) was out in two revisions; Rev 9, which initially shipped with the A4000, and Rev 11, which is the best you'll ever get. The Rev 9 part has two bugs that can cause problems with Zorro III cards. One can affect some kinds of bus slave cards, it depends on the card design. This is due to a small flaw in a synchronizer stage in the Level II chip (Level II runs a slightly faster bus protocol than Level I, and also supports burst). The other is a flaw in the Zorro III bus arbiter -- there's a small window in which a Zorro III slave cycle just starting can confuse a bus registration command, locking the bus. Rev 11 solves both problems, so you need it for DMA devices. The Rev 9 problems were fairly well qualified, so you have some devices that offered work-arounds. I didn't for the A4091 -- at the time, C= probably wouldn't have let me do the Rev 11 chip if the A4091 could have worked at all in existing A4000s.
As I understand it, an A4091 wouldn't work reliably with a Buster 9 but you might have been lucky.
