Another thought would be to try the OSS drivers. I used the older OSS drivers in a linux laptop that used a second sound driver for the on board modem. I was able to work around an IRQ conflict between the modem/sound drivers by using the OSS drivers instead of alsa
The OSS website has not been updated so I do not know if the OSS drivers work for more recent OpenBSD version.
http://www.opensound.com/openbsd.html