If memory serves, there were some issues with the WinAmp MP3 decoder doing a bad job, but from memory that was around version 1.8 or so. I heard criticisms on and off since then so I don't know (and I imagine they would have fixed this up now). But if I were wanting quality decodes to WAV format then I'd use LAME.

The WinAmp decoder was built for speed, like PKZip.

Have fun,

Paul