No, it's not a combination. All three are independent of each other.
3 channel amps
I assume 3 channel amps are for running a center channel? Is the 3rd channel a combination of left and right? Looking at a used Classe CA-3200
3 channel amps
I assume 3 channel amps are for running a center channel? Is the 3rd channel a combination of left and right? Looking at a used Classe CA-3200