Had a bit of issue re-routing all sound through HDMI.  Here is the fix:

create or edit /etc/asound.conf, and here is the only line in my file:

defaults.pcm.device 3

Run the following command, and note which device your HDMI output is:

~$ aplay -l **** List of PLAYBACK Hardware Devices **** card 0: NVidia [HDA NVidia], device 0: ALC662 rev1 Analog [ALC662 rev1 Analog] Subdevices: 1/1 Subdevice #0: subdevice #0 card 0: NVidia [HDA NVidia], device 1: ALC662 rev1 Digital [ALC662 rev1 Digital] Subdevices: 1/1 Subdevice #0: subdevice #0 card 0: NVidia [HDA NVidia], device 3: NVIDIA HDMI [NVIDIA HDMI] Subdevices: 1/1 Subdevice #0: subdevice #0

In xbmc preferences->system->audio ouput device & passthrough device…change to custom, and enter manually your HDMI ID.  Mine was:

hw:0,3