Your Onkyo M-504 is one of my favorite amps! Very nice set-up you have there.
I grabbed a pair of Polk Rt-25i speakers to hold me over until my first set of Axiom M3Tis arrived. Circuit City sold the Polks for way under MSRP, and they were very nice little speakers, especially in light of the about $100 they cost for the pair. Polk makes some nice speakers.
I personally prefer the Axiom M3Tis to the pair of M22s I had, maybe it was just a bad luck pair, but they definitely sounded thin. I've since picked up some cousins of the Axioms, Michaura M55s (twin 5.25" drivers and the 0.75" tweeter like the last-gen M2Tis) and they are to my ears awesome speakers.
You may want to try a pair of M3s or if you like floor standers, a pair of M60s.
PS, I've been looking for a nice M-504 for about 2 years. Picked up a Yamaha M-80 brute amp, but am still looking for the twin metered Big Onk.
