Funky, welcome. The Onkyo 605 should be an excellent choice for the setup that you're considering, regardless of whether you go with the M22s plus sub or the towers. The center speaker can certainly be the one to postpone, either using a "phantom" center or experimenting with one of your present speakers.
As to the location of the surrounds, if you're not going to use both side and back surrounds(7.1)they're still side surrounds even if they'll be a foot or so behind you. They should be separated a little more than the present 8' wiring locations, so extend the wiring maybe 3-4' wider to each side.
