I have the 630. No it won't give a separate or single back channel. The 2 additional "Rear" speakers will output the same thing at the exact same time with the scenario your describing. If you add speakers to the rear, I would advise that you just use 7 channel stereo or HK's own 7 channel decoding as it sounds much better...........best of all, it doesn't add a lot of junk to the source.....echo, delay etc etc.