I have been using an nc400 for the woofer and a THX789 for the compression driver.
This is by far the best amp combo I have ever used and the best sound I was able to get on the M2.
The THX789 has different gain settings on the front so you can leave the volume control at max position measure your gain from there.

I don't think there should be any problem mixing good amps. If you get a different magnitude or phase response around this kind of crossover region then there is a serious problem with one of the amps.

Anyway, throwing in more watts than needed is not a problem either, as long as you don't hear noise through these sensitive compression drivers, or risk too much watt in case of a crossover failure/mistake.