Arena 8600 on an Ultra320 adapter

We have an Arena Premium 8600 (16-bay) Ultra160 disk array
that works using an Adaptec 3960D Ultra160 SCSI adapter in a
Dell PE2600, or using a PCI Dual Channel Ultra2 SCSI Adapter
in an IBM RS6000/H70, but absolutely refuses to work with a
PCI-X Dual Channel Ultra 320 SCSI adapter in an IBM
RS6000/p615. Symptoms are a SCSI BUS ERROR (TEMP) about
every 90 seconds in the errlog, and a SCSI dstat:81 message
in the Arena serial port OUTPUT window. cfgmgr does not
recognize the array.

I have tried a different but identical array, different
cables/terminator, different Ultra320 adapter, reducing
maximum bus speed, and various reboots and array restarts.
The array slices are less than 1 TB each. The adapter runs
diagnostics without errors and an Ultra2 3580 tape drive is
recognized on the adapter without a problem. Adapter
firmware and AIX driver are the latest.

Has anyone else successfully used an Arena with an Ultra320
adapter? If so, how did you get it working?

Thanks.

Olaf