You really don't need to access the power amp section directly. Just set the volume control of the integrated amp somewhere and then adjust the surround processor to match the volume of all speakers.
My other preamp, a BAT VK-3iX, has a HT mode. It just sets the volume control to have unit gains. I am using the Dude preamp from TRL now. I just adjusted the Dude's volume control so that all speakers have the same volume.
My other preamp, a BAT VK-3iX, has a HT mode. It just sets the volume control to have unit gains. I am using the Dude preamp from TRL now. I just adjusted the Dude's volume control so that all speakers have the same volume.