I'd elect to run no center channel. In addition to finding a good physical match with your speakers, there are timing and clarity issues that, personally, I'd forego dealing with, instead focusing on solid multi-axis sound from your stereo speakers. I used to setup a lot of nice center channels, and it always paid huge dividends to get them well time-aligned with the mains. By time aligned, since this never was measured, I mean that we attained good vocal clarity, that any recorded Center Channel ambience produced in the L/R, like "room" that the voice was in, was clearly portrayed, that the center vanished, etc., all were things to be coped with. While I don't think there are rules to mixing center channel info, sometimes it was just a dry voice, no effects; my L/R can handle that.
Eventually, having turned-over product and brands in a fair number of demo theater systems, it became clear that mixing two brands wasn't any worse than a good salad or stew or soup or anything we enjoy made up of many ingredients. While eventually every demo system would become a demo of one brand, that period of time when new speakers were trickling into the existing system never was all that bad.
