ATAPISCSI hang error on install

System:
Tyan S2466, BIOS v4.05, GDT-PCI ICP Vortex PCI-RAID controller (main disks, RAID0) v6.08B, Broadcom 10/100/1000baseTX NIC, Sony CDU5211 CD-ROM (EIDE). On every boot, the sequence gets to:
pcib0 at pci0 dev 7 function 0 "AMD 768 PCI-ISA" rev 0x05 pciide0 at pci0 dev 7 function 1 "AMD 768 IDE" rev 0x04: DMA, channel 0 configured to compatability
pciide0: channel 0 disabled (no drives)
atapiscsi0 at pciide0 channel 1 drive 0
scsibus 0 at atapiscsi0: 2 targets

and hangs. No keyboard response, nada. Looked through the archives and found some hints about trying to unplug/disable E/IDE devices to get past atapiscsi bugs, no dice - on unplugging the CD-ROM _and_ disabling the controller (had to to disable, otherwise it kept detecting), it then hangs in:

pckbc0 at isa0 port 0x60/5
pckbd0 at pckbc0 (kbd slot)
pckbc0: using irq 1 for kbd slot
wskbd0 at pckbd0: console keyboard, using wsdisplay0 npx0 at isa0 port 0xf0/16: using exception 16

Same sort of hang. Can't even Shift+PageUp to get more complete dmesg data.

Troubleshooting already done:

Upgraded/downgraded BIOS from 4.02 through 4.05 (all available on Tyan page) one at a time
Moved CD-ROM from PRI to SEC and from MASTER to SLAVE on both controllers
Made (one boot at a time) IRQ and DMA changes as allowed by BIOS Enabled/Disabled IDE "32-bit access" with DMA changes as allowed by BIOS
Tried v3.0, 3.1, 3.2, 3.3 and 3.3-snapshot boot floppies (floppyxx.fs and floppyBxx.fs)

Nada, zip, zilch, nothing, no-way-no-how. Every boot it hangs and can't/won't continue.

-- 
Ed Vázquez

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