The default setting IS surround....I think. I put my ear to the back speakers and it seemed doing 5.1... You see, the mainstage is a virtual surround system but can be upgraded to 6.1 in the rear speakers. You just by another mainstagehd and you have a fully concealed system. I don't think it sounds like 2.0 stereo. I'm pretty darn sure it sounds like before. The instructions say:
Primary Pass through: Select if you connect this unit's digitial audio out AND hdmi out to a device with LPCM, DOLby Digital and dts.
The optical is going to my front mainstage hd, and my hdmi is going into my tv. So, that means I would uses the default, right?