Thanks to Nathan Williams!!

I re-id'ed the Syquest drive to device ID 0, reattached the USB (eUSCSI by 
Shuttle) and it now reports a drive not ready error (there is no cart 
jammed in it), and also gave hints that it read a CDB from the SCSI 
device, which looks like I should be good!! So the fix is that the adaptor 
only supports SCSI ID 0.

I just found out the honkin' big tape drive appears to be differential 
SCSI. Looks like I'll have to build or buy a converter. Progress though! 
(Drive is IBM 9348 as I recall).

Much thanks!