After a very busy 5 weeks I finished my project, complete with a pre-programmed midi controlled robotic track cam, video looping, DMX lights and more. I uploaded the video to YouTube at 2am this morning so I've finally got the time to update this thread. It turns out despite the Mac Pro I bought I did need to use the USB adaptor after all and it's in the video and worked great. Of course it was outputting a digitally zoomed webcam image at 480p so it doesn't prove anything. hehe
Actually now that I've used it more, I've found that full motion video does look crappy at higher then 480. But in SD it works great.
The reason I had to use it was the only way I could quickly figure to trigger Quartz Composer to Run was to use a program that converts midi to keystrokes (MidiStroke) and send a Command R but for that to work the Viewer had to be on top and therefore modul8 (I assumed but never tested) couldn't be in full screen on the main desktop, so therefore for my 2nd screen (the plasma not the rear projection) was coming from the DisplayLink.
Bear's Looptastic Spectacular - World Premiere:
http://www.youtube.com/watch?v=iNmjmSrrLUI