And for me, on the problem system, it says (fat-fingered by me):

  . . .
mainbus0 (root)
pci0 at mainbus0 bus 0: configuration mode 1
pci0: i/o space, memory space enabled
pchb0 at pci0 dev 0 function 0
pchb0: vendor 0x1166 product 0x0008 (rev.0.23)
pci1 at pchb0 bus 1
pci1: no spaces enabled!
pchb1 at pci0 dev 0 function 1
pchb1: vendor 0x1166 product 0x0008 (rev.0.01)
pchb2 at pci0 dev 0 function 2
pchb2: vendor 0x1166 product 0x0006 (rev.0.01)
pci2 at pchb2 bus 1
pci2: memory space enabled
pchb3 at pci0 dev 0 function 1
pchb3: vendor 0x1166 product 0x0006 (rev.0.01)
pci3 at pchb3 bus 2
pci3: memory space enabled
ahc1 at pci3 dev 5 function 0: unable to map registers
ahc2 at pci3 dev 5 function 1: unable to map registers
  . . .

The fact that pci1 has "no spaces enabled!" looks interesting, but 
the SCSI controllers seem to be on pci3, which seems OK. Does this 
give more clues or more confusion?

--Paul Hoffman