Mapman,
I have to say that all planar users should spend some time with ICE power amps regardless of budget.
They are a marriage made in heaven for full range planar speakers. Some ICE amps are better than others or suited to a certain balance of sound, but their ability to keep the panel under control and give you huge amounts of clean, undistorted power make them almost a miracle when you look back at what was available just some years ago.
I bet the MG20 sounds great with them as would all maggies I am sure. I would love to hear a Martin Logan CLS or CLX with them.
Regarding which size of amp to use on which part of the frequency range, I think Mapman is right. Use the cleanest sounding on the highs/mids and the other on the bass.
Call me an audiophile, but my worry would be towards the xover itself and the differing amps on such a capable and resolved speaker.
If you have the resolution you may find artifacts in the presentation especially with soundstage. Real recordings of ambience such as in orchestral recordings may loose that top to bottom unity. Something these speakers excel at. It would be dependent on where the bass cut off is and obviously if its very low you may get away with it.