3-monitor setup with Final Cut Pro

So I'm trying to figure out how to do external playback on my Sony TV while using my 2 main monitors to edit. Help anyone?

My setup:
I have a Mac Pro tower with 2x ATI 5770 graphics cards and 2x 24" monitors which are hooked into one 5770. My TV is hooked up via DVI to the other 5770. Both monitor are working great side-by-side and the TV is working well as a third monitor.

The problem:
When I go into "Audio/Video settings" in FCP, and set up the "Playback Output" to Digital Cinema Desktop Preview, like I read to do, the video plays back on my 2nd 24" monitor. How do i get it to play back on my TV instead so I can still use my 2 monitors side-by side? Thanx a lot!!!