There are a couple of performance difference that can
potentially crop up. Whether or not these differences will actually exist depends on the specific designs of the amps in question. Whether or not these differences will be
audible is another matter entirely and highly debateable!
The differences are: some multi-channel amps are able to route all of the power available in the power section into each channel dynamically. In other words, suppose the amp is able to produce 200 Watts into each of 5 channels simultaneously. Some multichannel amps are able to route that full 1000 Watts into a single channel on demand, or 500 Watts into two channels simultaneously on demand. In other words, if one or two particular channels call for a sudden, huge spike in dynamic power, some multi-channel amps are able to deliver that by essentially re-routing all of the available power into those one or two channels. Monoblock amps, meanwhile, will always have their rated power for each individual channel - no more, no less.
The second difference is potential cross-talk. With all of the channels in a multichannel amp sharing the same power source, there is the potential for cross-talk between channels to occur. In other words, the signal in, say, the Left Front channel might "bleed" a little bit into the Center or Right Front channel and if you put your ear up against the Center or Right Front speaker, you might hear sound that is only supposed to be coming out of the Left Front speaker (just as an example). Meanwhile, monoblock amps will never have any cross-talk - unless cross-talk occurs inside the processor.
The final difference is noise floor. This is not really a "multichannel vs. mono" design difference. But it is a practical difference that shows up in real world usage more often than not. Since a high power multichannel amp often has a larger power section than a monoblock that is rated to deliver the same power into each channel, you'll often have a higher noise floor with the multichannel amp. Put your ear right up against your speaker's tweeter and you'll often hear a soft hiss when the processor, amp and source are all turned on and connected but nothing is playing. You might just as likely hear a soft hiss with a monoblock amp as well - it really all comes down to the design and quality of the amp. But just in terms of likelihood and what is common in real world usage, you'll find more monoblock amps that produce extremely little or no hiss at all vs. multichannel amps that are rated to deliver the same power into each channel. The multichannel amps almost always produce at least a slight hiss. Some have a fairly substantial hiss.
So me, personally, I detest having a noise floor. I can't stand any level of audible hiss, hum, buzz or other operational noise. When there is meant to be silence in a soundtrack or song, I want to hear silence! I'm not going to the trouble of soundproofing my theater and acoustically treating it just so I can hear an operational hiss, hum, buzz or whir when the recording calls for dead silence! As a result, I tend to favor monoblock amps myself. You'll more often eliminate any noise floor with monoblocks and you'll never run into cross-talk. So long as the monoblocks have all the power you need to hit the dynamic peaks that you require/want, there's no down side to monoblocks - other than needing more receptacles and power cords
And FYI, you might want to also consider the Emotiva UPA-1 monoblock amps. I haven't tested the Outlaw 2200 monoblocks enough to know whether they are any better or worse than the Emotiva UPA-1, so this isn't any sort of "knock" against the Outlaw 2200 amps. I can merely vouch for the UPA-1 amps as being DEAD silent in the noise floor category and capable of very clean output a little above Emotiva's conservative specs. I'm not saying the Outlaw 2200 are necessarily worse or that the Emotiva UPA-1 are definitely a better choice - I honestly don't know since I've not tested the Outlaw 2200 extensively. But yeah, just saying the Emotiva UPS-1 FOR SURE are terrific monoblocks at an affordable price
