THP, another welcome. I agree with Tom that looking at your setup, it isn't the M22s that should be objects of "upgrading", but rather the center channel. With subs handling the low bass burden the M22s can still do the necessary work. As to power handling(above the bass)keep in mind that the M22s have two 5 1/4" drivers handling the all-important mid-range(as does the M80), while the M60 has only one. The result is that the M22s have more capacity there compared to the M60. The size of the enclosure has no direct bearing on this, it's simply the number of drivers handling that frequency range.
Of the receivers that you mention, the X4000 would be the better choice if within your budget, most notably because it has the top Audyssey MultEQ XT32, while the 727 version is two steps down with the MultEQ. A better buy at present though would be the factory refurbished Onkyo 818 for about $600 from Accessories4less