Newbie question for Marantz AVRs

[Beta Man]

I feel silly asking, but I tried searching online and reading the manual, and I just can't figure it out (although I did find the reason why my AVRs run hot all the time.... If you leave the "Multi" function on, one amp stays active even when the unit is off )

ANYWAYS.

I got my rear speaker (just one) and I also have an old center speaker I'd like to use to get 6.0 with my bedroom setup....

SO,

I'm trying to get 6.0 with my Marantz SR5001 and 6.1 with my Marantz SR7001

Here's the question.....

How should I connect the center rear speaker to get 6.1 (or 6.0 for the bedroom) for Blu-rays that have 7.1 audio tracks????

I don't want to connect the speaker to just REAR LEFT, or just REAR RIGHT, and only get one of the discrete rear channels, and lose the other.... I want to matrix the two rear channels down to one speaker (if that's the right term for it even....)

Is there a function to set the players (both PS3s) and the AVRs to, to send a combined signal, or should I run two sets of speaker wires from both the Left and Right rear outputs on the AVRs to the top and bottom binding posts on the speaker (in essence bi-amping I guess)

The problem with the bedroom setup though, is the center-rear speaker I'd be using only has one set of posts, so that would only be an option in my media room setup.....

Any Ideas on this?