I would agree with JohnK, save the money for speakers and wait on the receiver upgrade.
If there is something you absolutely need for your setup that is available in the new receivers only, then I can speak to the 507. It is more than adequate to drive any Axioms up to and including M60's, especially in a small room. Keep in mind that Axiom speakers have a wonderful sensitivity spec, and require less power than expected. I have had zero regrets with my 507, and was oscillating between the 507 and 607 before going the 507 route.
One thing to keep in mind about the 507 is that is does not upconvert any video sources. If you have any other 507/Axiom questions, just shoot.
EDIT: originally edited for spelling, but thought I'd add that saving on the new receiver will greatly benefit the inevitable wish to upgrade from M2's to M3's to M22's...
