VGA External Source, DL2

I have a fairly new, and hopefully robust, video system in our theatre. All of our video hits a BlackMagic Matrix, and can be routed throughout the building. I just got four old DL2's, and would like to send video to them. I do have SDI-VGA adaptors but can't get them to work (I've tried 800x600, 1024x768 at 30, 29,59,60 hz) I can tell the signal is getting to the DL@ because when I switch from internal to external source I can see, just for a moment, the content (although it is distorted, but its definitely the test contect). I'ce also tried just sending the video over directly from the video server (in this case a watchout box) bypassing the matrix, with the same result. so what am I doing wrong?