It may depend on you computer's sound card. If you can send computer audio out of HDMI than it should work with Wirecast External Display Output as well.

CraigS I have the Wirecast Gear Model: 110, does this system have a sound card that allows audio on the HDMI output ports? I would assume the gear should have this functionality but I have not been able to get this to work when outputting my content to these ports.

Aaron Hadley I'd think It should work. Consider one might use a monitor or HDTV with built in speakers. You'd want both video and audio to be carried.
You may want to check Wirecast > Preferences > General tab > Audio Interface field and see if changing a setting there helps

If not, Fill out the form and report the issue. 
Wirecast Gear Report Form