I have been all over this same issue in the past 3 years - 2 amps, 1 amp and 4 amps to run 5 channels! This is not an easy decision....
To run a Talon "Raven's Nest" 5.1 setup, I started with a 2-channel Pass Labs X-250 and 3-channel X-3. Though the sonic synergy with the Talons wasn't really there, the dynamics WERE terrific.
Next, and like Mr. Pixel above, I then employed a Titan running all 5 channels for the same speakers, and it was really great. It matched the Talons' sonic characteristics perfectly - smooth and natural, it's amazingly cool-running (efficient), provided a very deep image/stage, never sounded stressed even in *HEAVY* 5.1 use and was just plain easy to live with. I didn't realize just how good this amp was until I sold it...
Then, in my infinite wisdom, I surmised that 3 monoblocks for L/C/R and another running stereo for the rears *MUST* be better for dynamics and overall sonics then one good 5-chnl amp. To be honest however, I really gained nothing decernable except system complication - just more expensive cables, more rack space taken up, etc. And these mono amps are no slouch (Electrocompaniet AW220's).
Having said all this, I am now going to try to get back to a simpler middle-ground. I have a 2-channel Sim W-5 LE on order right now, intending to replace a pair of the monos to drive the front channels and use exclusively for 2-channel operation. If this works out well, I may jump on a 3-channel Titan to drive the rest of the setup (center & rears).
Keep in mind that ALL of my equipment has always run from ONE 20-amp AC outlet, feeding a single B-P-T 3.5 Signature line conditioner to drive all the stuff - including all the amps. I know this is not optimal, and could certainly effect the results here, but I can't add dedicated circuits to my environment right now. At least the power conditions have remained identical throughout these changes in amps.
I don't know if this will help in your decision, but I CAN tell you that the Titan has never sounded like an amp "compromised" by running all 5 channels in my system.
..... But YMMV .....
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