Lee, as you know, my own listening is almost entirely classical and I've suggested that 2-channel source material is heard significantly more realistically with surround speakers in use driven by an AV receiver using a mode such as DPLII.
Having said that, if you're going to continue using only front speakers, then my view is that using M22s plus an EP500(or similar), which is what I use, will give you a significant advantage in bass extension(especially relevant in pipe organ material)over even speakers such as the M80s and M100s which have relatively good bass response when used alone. So, I'd be in agreement with the trade that you propose.
As to connections, if you continue to use the stereo amp which has no provision for bass management, the sub would be connected to the output terminals in parallel with the M22s. The M22s would be driven full-range and the low-pass filter in the sub would be used to roll it off above the point(say about 60Hz)where the M22s roll off "naturally".
