Thanks Lucio & Richard. 

I've tried to boot via CD again (mind it's from a USB CD drive 
in case that makes any difference), but so far no success:

PBSR...0000 F5FD 0000 00B2
Plan 9 from Bell Labspcirouting: PCI.0.31.2 at pin 2 link 96 irq 11
disk loader

cpu0:  1662Mhz GenuineIntel P6 (cpuid: AX 0x06EC DX 0xBFE9FBFF)
ELCR: 0800
497M memory: 497M kernel data, 0M user, 18M swap
found partition #S/sdC0/data 0 123,091,920
disks: sdC0
trying sdC0...dosinit: can't open #S/sdC0/9fat
dosinit #S/sdC0/9fat failed

Boot from: sdC0!cdboot!9pcflop.gz
dosinit: can't open #S/sdC0/cdboot
dosinit #S/sdC0/cdboot failed

Boot from: sdD0!cdboot!9pcflop.gz
dosinit: can't open #S/sdD0/cdboot
dosinit #S/sdD0/cdboot failed

Boot from: local!/boot/bzroot
can't open partition #S/local//boot/bzroot

Boot from: local!boot/bzroot
can't open partition #S/local/boot/bzroot
------------------------------------------
9fans: 9fans
Permalink: https://9fans.topicbox.com/groups/9fans/Tb5aaf646618a421a-Mb8683148f4648b349adb5e06
Delivery options: https://9fans.topicbox.com/groups/9fans/subscription