Mark, you appear to have enough room behind the listening position to make back surrounds in a 7.1 channel system worthwhile. They should be mounted about 3' above ear level and separated about as much as the distance from the listening position, say about 6'.

Incidentally, on a point of terminology, if by ".2" you mean two subs, that remains .1 with two subs in the .1 LFE channel. The numbering(e.g., 5.1, 7.1)refers to the number of channels, not the number of speakers. There are no .2 channels formats, and a 5.1 system with two or four subs is still 5.1, not 5.2 or 5.4.
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Enjoy the music, not the equipment.