hi
Try playing around with the audio endpoint plugin. Get an event to trigger the AudioEndpoint.SetByName command when computer display time has reached critical.
or as a test make sure you can voice control vc, when monitor goes off, tell vc to switch over to hdmi.
<?xml version="1.0" encoding="utf-16"?>
<command id="434" name="audio hdmi" enabled="true" alwaysOn="False" confirm="False" requiredConfidence="0" loop="False" loopDelay="0" loopMax="0" description="">
<action>
<cmdType>AudioEndpoint.SetByName</cmdType>
<cmdString>NVIDIA HDMI Out</cmdString>
<cmdRepeat>1</cmdRepeat>
</action>
<phrase>audio</phrase>
<phrase> h d m i,TV</phrase>
<event>audio hdmi</event>
</command>