So ok, I'll take the learning hit. I'm kinda tired of my firewire output to video and then my audio not syncing in my preview monitor. I run out of my firewire for video into my Canapus 110 from there it's Svideo to the monitor, and the audio is run out of my sound card to the same bridge but I split it from there using a stereo to rca into my preview monitor. Either way, the video is choppy and the audio won't synce unless my vegas preview is on the lowest settings.

Will a SDI card fix my issue and give me the best possible synced preview to my preview monitor?

We use the Balckmagic Design HD Extreme card - does both SD and HD/SDI preview. Works fine with audio.Card can not capture/ingress with vegas 6.0 - even if Blackmagic site says so - only playback/preview and print to tape. Sync problems can be adjusted in the "sync offset" setting somewhere under options
/magnus