Well you're in for some cost benefit analysis here. So it looks like you've outlined 70% music, do you feel that your movie watching could benefit too? If not, you could simply go for a 2ch which usually gets you the best power/price (though, on emotiva which I'm most familiar with, their 2ch is more expensive than the 3ch).
This though will leave your center and surrounds (i assume by your mention of 5ch amps that you have a 5.x setup) on your receiver. A popular choice is to go for a 3ch, to be used with the front speakers while leaving the surrounds powered by the receiver. I personally view this is probably the best option when not in the largest of rooms. The surrounds, not being the most critical of channels, will probably be just fine with whatever power the receiver can give to them, additionally after offloading the other 3 channels there will be more power reserve for dynamic peaks on the remaining two.
If you wanted to go for the gusto going and were willing to $$$ there's nothing wrong with going for a 5ch