Just a thought - if you're planning to have a central install with cat6/HDMI (and audio) to all rooms - why not have a decent server grade main computer with 1 virtual machine for the core and one for each MD? You'd have to add a graphics card for each MD, but that's way cheaper than a full MD.
Another thought: What do you plan to control your MD with? If you only plan for a mobile orbiter, like iPhone/iPad/iPod/Andriod/ then it's no worries, but if you plan to use an IR remote, you'd have to have an IR receiver and rout that info back to the right MD.
/Joakim