I'm setting up a media room based on exactly the same principle as mentioned by the poster above. I started out buying all matching speakers (KEF R-series) but later decided I wanted to upgrade my main L&R to Dutch & Dutch 8c's. They don't make a center channel and buying one to use as such is impractical (and maybe not possible anyway). So I'll definitely be testing the school of thought that matching brands is not super important with even the center being another brand. I'll be using a Lyngdorf pre/pro with their proprietary room correction called Room Perfect. Total of 15 speakers plus subs.
I should note that my priority with the room is music (2-channel and possibly multi-channel) so the center will only be used when in theater mode. If it's too noticeable I can try using a phantom center. My seating is just one enormous sofa so I'm not too worried about different seats having a problem with dialogue.
The D&D's are uniquely equipped to handle what would normally be the acoustic issue of having a 100" flat screen tv between them (they're highly directional). They also have their own room correction that'll come in handy when listening to just them.
I'm still in room prep mode so I'm anxious to get everything going.