I have exactly the same problem on current amd64 GENERIC.MP.
I follow instructions from: http://www.openbsd.org/faq/faq2.html#Bugs
and I find:
#grep "<azalia_codec_find_defdac>:" azalia.dis
0000000000002600 <azalia_codec_find_defdac>:
0x2600 + 0x91 == 0x2691
#more azalia.dis
../../../../dev/pci/azalia.c:2352
2689: 48 63 53 28 movslq 0x28(%rbx),%rdx
268d: 48 8b 43 20 mov 0x20(%rbx),%rax
2691: 8b 34 90 mov (%rax,%rdx,4),%esi
# cat -n azalia.c | head -n 2352 | tail -n 1
2352 index = w->connections[w->selected];