Hi 1961TC4ME,
Although I have not personally tried this yet, it sould be possible.
I connected my 40 inch plasma to my Mac Mini with a HDMI lead, and in the sound setup I was able to choose between the inbuilt sound card or the the 2 channel "LGTV" as the output.
Therefore - audio over HDMI works for me.
I do not see why you could not use it in 7.1.
I suggest to power up the computer and 7.1 HDMI amplifier before starting Hauptwerk software. This way Hauptwerk can start with all audio outputs ready to be selected in the setup.
regards,
Matt