For the scenario you describe you'd probably want to get the Sony PS3 BD Remote. It has plenty of buttons and uses Bluetooth, which your Mac Pro most likely already has built-in (=> you can check in System-Profiler.app).

While you can configure Remote Buddy to issue custom keystrokes, execute Applescripts and more for every button of the remote for every application, you usually won't have to do that: Remote Buddy already can control over 100 applications out of the box.

Best regards, 
Felix Schwarz