That's right in the middle, of course, meaning that an unambiguous answer isn't obvious.
According to the Owner's Manual for the 4311, its power supply is rated at 790 Watts.
Emotiva's X series amps all have power supplies rated at 1500 Watts, whether they're 1, 2, 3, or 5 channel.
Outlaw's 7500 has a power supply rated at 1700 Watts.
There are two major effects which are helped by using more powerful amplifiers: distortion and volume level.
When you drive a speaker at a power level that's more than (typically) about 2/3 of an amp's rated power, the distortion starts increasing rapidly, eventually to levels that can be audible as you approach the amp's rated power where clipping starts.
Having double the power available for a given channel only increases the maximum volume level by 3db. Unfortunately, although it's a noticeable difference, it isn't substantial (our hearing is not linear). For a discussion of power vs loudness, see http://www.gcaudio.com/resources/howtos/voltageloudness.html
Given these two considerations, I'd suggest getting one (or maybe two) of Emotiva's 3 channel amps instead of one of the 5 channel amps you've been considering, and let the 4311 drive the remaining speakers.