The positioning will almost definitely affect the sound in some way, but it doesn't sound like there is a whole lot you can do about it. It is possible that you'd be better off with M22's on stands, especially since you already have subwoofers that you are happy with.
As Randy mentioned, some folks have had to endure suboptimal placement and still really enjoyed their speakers. Others have placed even tower speakers (like the M60) on short risers to mitigate such effects (tarted-up cinder blocks or similar).
If the 605 has Audyssey, that might really help with those placement issues, too.
Have you considered distributing your subs around the room? Co-locating them (as you've done) will maximize the gain, but you might get more even and more pleasant response from experimenting with placement, if that is an option.
