I was talking to Outlaw and they suggested that with 5 8 ohm speakers I should keep the 1050 set at 8 ohm when adding a pair of 8 ohm speakers in parallel for rear center. The 1050 manual says to move the 1050 to 4ohm when putting the rear center pair in parallel.

Does this sound OK?

I'd suspect it's a thermal budgeting sort of thing. In any case the tiny amount of avaerage output from the center rears probably won't warrant switching the whole thing to 4 ohm mode.