Can displaylink be only monitor

[chmedly]

I have a 2008 macbook pro that had a faulty screen so I removed it and have been using it as a headless server for awhile. Last fall I bought a displaylink based usb to hdmi adaptor and did some experimenting. I found that it could pass audio passably, which is what I was mostly looking for at the time, but that video playback was not good. At the time I found that the computer won't boot unless a display of some sort is connected to the DVI connector. What I've been using is an Apple DVI to composite adaptor as a dummy plug. This allows the computer to boot. More recently I decided to use this computer as a desktop computer with the usb -> hdmi adaptor and had it working fine for a couple weeks. The HDMI screen was the primary and only screen. Then, after some software changes (plex media server) the machine froze and when I rebooted I discovered that the computer was sensing 2 monitors. The built-in video card was working what it thought was a composite display and the displaylink screen was the other. Now I can't figure out how to "remove" the composite one so that the only display in use is the 1080p displaylink one. Any suggestions? btw, this is with osX 10.6.8. I am hoping to move to 10.9.2 soon but it's looking like there might be some issues with the displaylink drivers with Mavericks...