I can't honestly see myself purchasing anything above a mini-ITX style motherboard for a media director. Because when you cross into the mATX or ATX style, not only have you increased the SIZE of your Media Director 10 fold, but you've also increased the noiseness, and the power consumption.
I HIGHLY recommend mini-ITX or nano-ITX style motherboards if you can get away with it. You can still get all the features you really need or want out of a mini-ITX board. Nano-ITX boards suffer a bit on available features yet, and Pico-ITX style have a bit to come since they only contain the basic output features.