Probably it is, Paul. The basic point is whether there's enough room behind the listening position for a back surround effect to develop. There's no rigid requirement, and users may be satisfied with different levels of results, but a 4' rule-of-thumb minimum is often suggested. If it would be tried a 7.1 rather than 6.1 setup would be suggested, to allow for the stereo back surround processing which DPLIIx, Logic 7, etc. can do with either two or five channel material.
It may be more cost-effective to have the side surrounds a foot or so farther back than the listening position to help give a little back imaging.
