A friend has the VP50 (I have the Edge) with its OSSC, the sound goes through hdmi. Check the audio parameters (audio input for example).
It has a FullHD TV and pc screen (monitor), often everything goes up to x5 (ossc+scaler).
In the DVDO (Edge or VP50 almost the same) you can take inspiration from this:
The post of “Jacko”, settings on a yellow background.
Very important 2 parameters:
1/1 FRAME RATE: enable / disable enable
OUTPUT FRAME LOCK: autolock / unlocked unlocked