An alternative is to directly record the audio via a cassette deck phono audio output. A high quality deck with SPDIF output would be ideal if you have an SPDIF input.
It's possible the digitizer you bought transfers at high speed. You would lose the speed with audio recording and have to edit extraneous noise at the start and finish. If you use a high quality cassette deck I doubt you would lose much quality over a cheap digitizer. I would record as a wav, convert to mp3 for everyday use and burn the wavs to DVD for the future. Nobody will want to play low bitrate mp3 a few years from now!
If you use the digitizer's namesake, AudioLava in your PC, I think that will split up the tracks for you automatically. There may be freeware apps that do the same thing.