correct recording level with Terratec Phono Preamp

I'm converting my old vinyls to CD, using the Terratec Phono preamp.
What is the optimal recording level (in dB). How do I find the optimal
combination between input level (setting min/mid/max on the preamp)
and the "volume" slider in windows recording control. (I assume the
higher the input signal and the less internal amplification the better
- unless the input signal is beyond what the soundcard can convert -
how to find out) Has anybody done the same and some advise/hints?
thx and enjoy
Bruno