Audio cleanup?

While my Japanese class is going well so far (the pace is a bit slow, due in part to the overhead of community-college drop/add handling), I’ve found one serious annoyance: the audio CDs are crap.

There’s nothing wrong with the content; the material is presented clearly by native speakers, and the original mastering was well-done. Unfortunately, it was mastered for cassette tape, and the CDs were apparently converted from that format. How well was this done? Here’s a thousand words on the subject:

Situational Functional Japanese Audio CDs

That’s what it looked like when I loaded a track into Audacity. I can crank up the gain, but then the hiss becomes objectionable, and Audacity’s noise filter introduces some rather obnoxious artifacts, even at its gentlest setting. I’ll be using these CDs until March, so it’s worth a little time and money to me to get them cleaned up. Any recommendations for a good tool?