Audio-only Cature with Plextor ConvertX

I have a Plextor ConvertX, and I love it for video capture. I have a few audio cassettes I need to digitize, and normally would just run them line-in into my cheap-o soundcard. I was hopeful I could find a program that would recognize and lift audio via the Plextor but thus far have had no luck. I can record video, save it to mpeg2, and then lift the audio, but this is a pain, plus I am not sure the resulting audio is of good quality.

Is there anything out there that will recognize the Plex and record audio-only from it, preferably into .wav?

Thanks for reading -

c.

Why do you think the Plextor’s sound chip is superior to your onboard one?