Hello! What's your host OS?
At least for Linux (host)/NetBSD (guest) this works:
-audiodev alsa,id=snd1 -device ac97,audiodev=snd1
In guest NetBSD this is needed for smooth playback:
sysctl -w hw.audio0.blk_ms=100
I'm typing this by heart and may not remember exact syntax, but it definitely works, I used to use an emulated sound card in QEMU for NetBSD from Linux.