Two Preamps Into 3 Channel Amp

I assume then that the best option would be to use the receiver to power the center channel then and just use the left/ right inputs on the amp from the str preamp? 

The denon receiver only has rca preouts so that currently goes into the center channel on the mca 325 amp. The left and right preouts of the receiver are going to the ht input on the anthem str preamp. Im using the xlr outputs from the left and right str preamp outputs to left and right xlr inputs on the mca 325 amp.  So I am using the rca input on the center channel of the amp and the xlr inputs for left and right channels of the amp.  I am getting some faint buzz from the center channel, but can only hear it about a foot from the tweeter at ear level.