Rock, I see that I responded to you
here when you were first considering your setup. Although for the most part you decided to go in a different direction, I can repeat what I said there.
I, along with Alan and quite a few others are of the view that the M22/EP500 combination is superb for the enjoyment of music(probably about 99% of my listening). I see no good reason to consider the M60Ti. Keep in mind that the all-important mid-range is handled by two of the 5.25" drivers in the M22, compared to only one in the M60. This indicates greater mid-range dynamic capability for the M22 despite the(meaningless except in the low bass)larger M60 enclosure.
The distortion that you mention at certain levels(not exceptionally high levels from the measurements you made)might possibly be due to a defect in one M22 or one channel of the NAD, so the suggestion by Tex(Mojo)to try listening to just one M22 may be useful to check this possibility. Your NAD is rated quite conservatively at 80 watts and in good operating condition can drive the M22s to dangerously(to your hearing)loud levels.
The problem with having to drive the M22s full-range, which may contribute to the problem, indicates the unsuitability of the NAD(or any integrated amp without bass management circuitry for a sub and mains)for your setup. You make a reference to a coming "5.1 receiver" but give no details. If this means that you're getting a new multi-channel HT receiver with bass management circuitry you can relieve the M22s of the lowest bass burden by setting the crossover to 80Hz. This can't be done with the EP500 control incorrectly labeled "crossover", as it's simply a low-pass filter which rolls the sub off above the selected frequency, but which can have no effect on the connected M22s.
So, if you're getting a new receiver the M22/EP500 combination should continue to be excellent and it would be suggested that you use wide-dispersion side-surround speakers such as the QS8s for both music(using a surround mode such as DPLII to hear ambience from the surrounds where it belongs)and movies.
