Hi Brian,
In-order to use the DeckLink HD Extreme card with Vegas, you need to down grade your DeckLink driver to V5.6 (driver can be downloaded from Blackmagic WWW). Remove your V6.xx, install V5.6 and restart the computer. Your Vegas should able to recognize the DeckLink HD Extreme card. FYI, up to now, V5.6 is the only driver that works with Vegas (not …V5.5 nor V5.7…). I had the same problem before.
Good luck
CreativeFans