AFAIR I had a TMC-850MEX included with my first Toshiba XM-4101 CDROM. The one I had lacked a BIOS and for DOS only CDROM drivers were available. Might've worked in Win95 with a general SCSI driver, but it got replaced by a much better NCR810 before that.
Check if your 850 has got a BIOS (28 pin DIL EPROM chip). If it doesn't and/or doesn't show a POST message on system start, then it's the crippled version.
If I'm not mistaked, I might have an old Adaptec AHA-1540 that also worked in 8 bit mode (probably sloooow) - I'll check that, but am afraid, I can't test it any more...
[...]Checked Adaptec's docs: it seems it's not compatible with 8 bit slots. Also found an AHA-1520 (PIO instead of DMA), but that one won't work either.
You'll have to salvage a 16 bit ISA slot from an old PC mobo and add it to your A2000, I'm afraid.
