Good point. There's some psychology to be thought about here.

You need an element in the picture that is of a known scale. The couch is pretty good, but maybe include something on the wall so you can compare the two... a door frame is the best I can think of, since they are pretty standardised.

I don't know, I kind of like the sofa. Standing behind it you can take in the whole room, not just the compare the screen with the speakers. Besides, this was the coolest photo I could buy. :)