Hi Tor, I have that same Matrox card and with 3 dispays, it’s setup as all three as one desktop or 2 as desktop and one as secondary.The later will allow you to use the secondary as full screen preview. Vegas wont see the HD output like Avid Media Composer so I drag my preview window to one of the 3 desktop screens and strech it to fill the monitor. I havent used the S video out so I don’t know how that looks. I dought it will look anything like if you send out IEEE-1394 and use a camera to comvert it to composite. Hope this helps,
Danny Hays