Ok so I have never ran a multi channel amp, only mono amps to my subs. And a bit curious about them, what the advantage would be.
In my blazer I run an alpine deck (think its a 50w x 4) with sony xplod speakers (and forget which ones i put in the dash ) and an alpine mono amp and alpine 10" sub.
In my vibe i run a kenwood ddx-418 (22w x4) with JBL Gto speakers, I wired out the factory amp, running an alpine mono amp with the same alpine sub from my blazer ( Vibe = summer car, blazer = winter car) so i switch the sub back and forth between the two cars.

In the blazer the mid ranges all sound perfectly fine and I can turn it up as loud as I want. In the vibe 95% of the time its fine and as loud as I want but I have found the max on it where the speaekers start to crack and get distorted, now is this a limitation of the speakers or limitation of the power supplied to them.

What is the advantage of running a multi channel amp for the speakers, and what would you run and how would you hook it up if you continued to run the mono amp just for the sub?

 

In my truck I run a jl audio 300/4 that runs my door speakers (infinity referance) & a 1100 alpinealpine mono amp powering a alpine type r 12 & love it. So that's how I did mine. I hope that helps some.

 

using a multi channel help gives you better crossover points for your speakers. louder and more clear if you know what your doing.