Between what I think your question is and the two answers, I'm kinda confused. I read that you want to go from 7.1 to 5.1 by removing your rear surrounds. I'll just babble on with my thoughts.
By going to a 5.1 system, your current speakers will work well on the side walls, slightly behind the main seating area (couch). They should be a couple of feet above the sitting position and face outwards or slightly forward.
Shelves are good. Very good.
Bipole/dipole speakers will go well in that same position.
Just a thought: Since you already have them, you could mount TWO of the speakers, back to back, on one shelf. Connecting them in series will double the impedance (a safe bet) but connecting them in parallel will half the impedance (check to see how well your amp handles this first)
You can make
DIpolar by connecting them
OUT OF phase.
You can make them
BIpolar by connecting them
IN phase.
Generally, dipole speakers are preferred for movies but there's no law that says you can't use bipole speakers. Heck, you can switch 'em around to see what you prefer.
Remember, aside from the shelves, this is a no-cost option.
Here's A better explanation than I gave you.