By confirming connections, etc. I think the problem is solved. I understand about heat - the DVDO vents are clear and the Comcast box is a newer one that does not get that warm. The previous Comcast box got very hot and the DVDO worked fine. I leave the cabinet open so there is adequate ventilation.
I take the output from the DVDO into a powered splitter, which after tweaking the connections, seems to have been the problem. Initially it was touchy and one of the two split channels would lose audio, then the other would lose video. Once secured all seems to be fine now.
Thanks for all the help and suggestions.