My understanding is that it is a range expander, not a compressor. Theory/thought being that music is compressed...recording teqniques using reduction of transient peaks, compression of loud levels, and upward manipulation of soft levels. Range expanders are supposed to try restore those ranges. How well it does that I'm sure is a fun debate. As I said, Im just playing around with one and I think it does well in moderation.
That being said I've never heard a stereo really reproduce live music well. Not to the point you can't tell the difference between live and recorded. The sound of live music has so much going on between highs and lows of different musical instruments plus the effects of sound distance and refraction that I don't think any two channel recording will ever (at least not to this point) be able to faithfully reproduce it. But, we do the best with what we have, hear what we hear, like what we like, and tinker toward the currently unobtainable.
W.