According to this post:
Re: Hauppauge HVR-1500 HD TV card
Got it to work, ATSC only, no analog. Use Ubuntu 8.04, and install the latest
drivers from LinuxTV.org. Use very latest Me-TV to autoscan and watch.

You are out of luck with the approach you want to try.

I have my stereo connected to my sound card in both directions. I've recorded
from vinyl using Audacity. Mind you, it takes longer than just downloading an
MP3 using bit torrent...