Two Preamps Into 3 Channel Amp

You can use the MCA 325 to power the center channel. But how you connect the front L and R channels? Do you have two pair of front L and R speakers, one pair for HT and the other pair for stereo playback?
It is OK if the XLR and RCA is not connected to the SAME power amp channel.

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.

I am getting some faint buzz from the center channel, but can only hear it about a foot from the tweeter at ear level.

One thing you can try to eliminate noise from center channel is insert a Jensen Transformers PI-RX

https://www.cs1.net/products/jensen_transformers/PI-RX.htm