Although the power of your receiver is being touted as 'pretty good', you are right to think about the rest of the receiver and its innards/build quality/technological quality.
I had a $1500 Technics system from 10 years ago that could not hold a candle to the new Onkyo DS797 that i recently bought. The Onkyo actually made my old Technics speakers just come to life (as much as they could). I can't even begin to explain the difference that changing the receiver made. Literally night and day.
I have to add that i CANNOT say the same thing about any other component i've changed in my system!! Not even the Axiom speakers (my old technics speakers were 6ohm bookshelves so making a comparison to M60s isn't right but other than the boominess and slight scratchy upper sounds they were far better than i ever realized).
However, to rule out your receiver as a garbage in/ garbage out component, head down to your local big box store like Best Buy, Future Shop, etc., and pick up a $500 Sony or Yamaha receiver and bring it home to test it out. If the receiver doesn't make much of a change you can always bring it back a day or two later for money back credit. I've done this a couple of times to test out cd and dvd players before committing a permanent purchase.
Of course you may want to look into other more simple fixes first just to be sure it isn't something simple like wires hooked up in opposite polarity, etc.
In my limited experience with these Axioms so far, they sure are not friendly to bad or 'hot' recordings or low quality peripherals. It shows, it really shows.
On that note, several people have asked similar questions in the forums lately about the same topics you are interested in (such as how much power do i need, what are good brand name receivers in xx$ range, how far should i place my speakers from the wall and are other people using the M50s finding they are boomy, etc.). Try doing some more general searching on the forums and you should find alot of answers to your questions.
The forum readers may also help point you to some specific links as well.
