I downed the official 5.8 when it came out, and had been using it for some months. I noticed that on John Petrucci's "Damage Control", that at about 3:30 in, he has a part where he gives two quick chords, followed by silence, and then repeats both. On 5.8, there is an instant of very loud output after the silence both times. This indicates that heavy compression can be heard on it. On re-listening to it, I found that I can also hear other heavy pumping artifacts.
Modern music production professionals often decry the overuse of compressors. It limits dynamic range, and introduces said pumping artifacts. It can also cause unwanted over-amplification of the noise floor. As to just what the appropriate use should be, varies considerably by taste, but overuse and misuse are often a sign of an amateur production. This is not to say that Winamp should apply no compressors, but that they must be optional, if used.
When I play "Damage Control" and hear those artifacts, I've pointedly disabled anything that should be able cause it. My output plugin is Direct Sound. My DSP/Effect is "(none)". I've temporarily disabled "Use Replay Gain". The equalizer and limiter are disabled on the Playback|Equalizer tab.
This is a stopper for me. I posed a message about this in the Winamp general discussion yesterday; but it hasn't as yet been approved for posting. I don't detect the problem in WACUP. They say that 5.8 is their final desktop update; but it appears to be fatally flawed in this regard.