can bipolar surround speaker on backwall with 5.1

If you haven't already purchased the receiver and speakers I highly recommend a 7.1 HDMI receiver and seven matching Sync One B's or smaller speakers and a sub. If your couch backs up to the back wall the rears would mount in the upper rear corners on the side wall pointing down at the listening position. Mount the the sides at ear level next to the couch. The L and R at ear level and on the same plane with no toe in as close to the display as possible with the C either over or under the display on plane with the L and R. With the calibration mic at the listening position let room correction do the rest.

No room is too small for 7.1 and matrixed 7.1 sounds better than 5.1.

You can mount a Dipole speaker for rear surround just fine its all up to you. The comment about not being able to use a dipole is silly, dipole surrounds radiate from both sides not front rear.

if the other half is picky enough to reject flush mounted, same color in-ceiling speakers, which aren't any more noticable than an HVAC vent, then How's she about the rest of the bulky speakers (including the ones you plan on mounting on back wall) and the rest of the electronics?
If that's the case, there's always the "Stealth" speakers and other invisible, surface integrated speakers, which completely dissapear into the wall!
I suggest ditching all the AV gear cluttered around the room, and simply go with an all in one sound-bar that's been excellently executed by numerous manufactures of late! They sound great, integrate all the necessary speakers, seriously reduce clutter and simplify, and look much more streamline with your monitor.
It just doesn't sound like all that gear strewn around the room is going to earn you any bonus points at your place, status quo.

Since I didn't read your well written room description closely my suggestion of surround and rear speaker placement is not correct.

My HT room is similar to yours except my 60" display is in a corner which would seem even more awkward for a good surround presentation but the Pioneer room correction is amazing. My description of the L,C, and R, are as I described above. My surrounds and rears are mounted very near the celling aimed at a 3' wide sweet spot. each of the surrounds and rears are at different distances from the listening position.

Previously I had a 5.1 Integra system which seemed to work well but upgrading to 7.1 with room correction has created an outstanding sense of surround which comes mostly from 5.1 media. Replacing the towers with matching speakers and adding a hidden sub will be much more fun with much deeper and controllable bass while giving the system a more sensible look.

Chadnliz, Queefee and Vicdamone. Thanks for your suggestion. Really appreciate it.
I went to a dealer during weekend and describe the floor plan of my living room. He, too, suggest me to use in-ceiling speakers. If this can't be done, he suggest me to use a pair of uni-polar speaker at back.