How can I use a external amp for center channel?

I am using external amps for all channels on my rxz11.all channels are covered except center channel.all the amps are 2 channel amps and the center channel is mono.can not find a good yamaha mono channel amp.i have a m80,m85,mx1,b6,m2,mxd1,mx1000u to choose from.can any of these be used for center channel?
Better yet, if the speaker is bi-wirable, just put one channel to top and one to the bottom ,of any of the stereo amps..
I take it that you've already tried hooking up the center channel speaker to your receiver, rather than through an external amp? If not, that's something you could try for free, and see if it works OK for you.

dont know if it is bi-wireable can you explain?I want to use one of the external amps to get more power to the center channel.when using the rxz11 as a pre amp mode it reduces power to the internal jacks to keep it from overheating problems according to manual.thanks for any help