Don't know if this is the case, but might be issue with the A3000 SCSI controller chip. A3000 loads Kickstart from HD too (mine did, anyway). That' why A3000 owners don't like changing hard drives. More of a headache to set up a new boot disk than you might think.
A3000 SCSI were pretty early, were never tested properly for SCSI ultrawide (which itself came in several variants to begin with). True Ultrawide is 32 bit data, LVD. Not single ended, if you want it all to work at LVD speeds , it's all got to be LVD (including the controller). Mix in one single ended device and it becomes pointless to use faster devices.
If the V6 adaptor assumes your controller is always true ultra wide, and doesn't drop down properly (particulary with the 3000 controller) that might be the root cause of the issue.
If it drops down and works OK with other early SCSI-2 controllers, that would seem to point at an incompatibility specific to A3000 onboard controller. And remember, a SCSI bus is always limited to the slowest device standard - any slow drives or devices limit transfer rate of every device connected on that bus. Including controllers.
