A few data points...

I've been using an NCR based controller on my 486DX2/66 (Cyrix) 
ASUS SP3G motherboard for over two months without problems.

I've also used a BT-946C simultaneously in this system without 
problems (as I type this the tape drive and a couple of disks
on the BT and the rest of the disks on the NCR).

One thing to be sure of is double check that all those wonderful 
motherboard jumpers are really, truely, completely correct.  Failing that
...who knows?  All the usual SCSI problems...bad termination, mixing
SCSI-1 and SCSI-2 devices on the same bus (most things do okay, some things
deal poorly), etc.

Second...

BusLogic numbers:

	Tech Support:	408/492-9090 (8-5PM US/Pacific Time)
	TS BBS:		408/492-1984 (9600 8-N-1)
	TS Fax:		408/492-9118
	Order Line:	408/492-9090 (software and manuals)

Note that current firmware/BIOS revisions are important on the 946C at
least...at least 4.22 firmware and 4.86 BIOS.

(I know, NetBSD doesn't use the BIOS, except at boot, but there it can
matter and break things).
--
Mark