Well, some quick comments on the BT946C...

I just put up one of these in a BSDI box (using the AHA1542) drive.
I had few problems...execpt:

The PC's are the new DEC PCI machines.  Their PCI isn't quite up to 
snuff...they autoconf the rom address but not the IRQ.

To get it to work, I had to enable the PCI slot, set the IRQ (I used
15) on the slot, enable the slot for bus mastering, go into the
card bios, and set it to the matching IRQ.

If the IRQ was wrong, the symptom would be the machine would boot
all the way through the autoconf stuff (because the probes poll), but
would hang (time out or just hang), on mounting root because that
is when the card would start to be accessed in non-polled mode.
The card would probe at the IRQ set in the card, but if this didn't
match the IRQ set on the slot...tough nuggies.

Good luck though, the card is fast, even in 1542 compatibility mode...
-- 
Mark

------------------------------------------------------------------------------