nVidia HDMI audio

Check which hardware devices are avaiable:

sudo aplay -L

Check which device monitor is connected to:

speaker-test -c 2 -r 48000 -D hw:1,3
speaker-test -c 2 -r 48000 -D hw:1,7
speaker-test -c 2 -r 48000 -D hw:1,8
speaker-test -c 2 -r 48000 -D hw:1,9

Pulseaudio automatically loads first hardware device(0,3 or 1,3). Manually load another in /etc/pulse/default.pa:

load-module module-alsa-sink device=hw:1,7

Source: ftp://download.nvidia.com/XFree86/gpu-hdmi-audio-document/gpu-hdmi-audio.html