I would go the other route.
Bypass usb audio altogether. Purchase a phono splitter to 3.5mm jack (£1.15 inc postage)
Plug the red and white phono cables from your camera into the splitter and insert into your "line in" in the audio card slot at the back of the pc.
Enable "line in" on your pc again and then change the audio setting in your capture software to "line in"
phono splitter:
http://cgi.ebay.co.uk/3-5mm-stereo-jack-to-2-X-RCA-phono-adapter-splitter-UK_W0QQitemZ360249294247QQcmdZViewItemQQptZUK_Computing_CablesConnectors_RL?hash=item53e087fda7