The audio is ahead of the video. The unit I provided (via the link) will only jump in increments. 50ms, 100ms, etc. That makes me cautious. It is also RCA -10 so I would imagine I would have to convert from +4 to -10 and then back again because my cable runs are XLR. Not 100% sure on the best practices for that.
I was also looking at a Behringer that is an EFX rack unit that has +4.
http://www.sweetwater.com/store/detail/FX2000
Some part of your video processing is adding latency to the video signal - likely a switcher/scaler. If you get more specific with your signal chain, I could probably tell you how to fix your problem without buying anything significant. Worst case you really only need 1 device as the delay should be the same for each speaker.
If you are working in a really large room, you need to have reasonable expectations for audio/video sync, as the speed of sound and the speed of light are pretty different. That 50ms increment is pretty workable as far as lip sync goes. Keep in mind that 30' back from the display your ears are going to hear the sound 30+ms after the light hits your eyes. If you can get it within 20ms, I don't think anyone would be able to tell the difference either way.
Don't buy that behringer - it's not really designed to do what you are trying to do.