A few settings you should know about that have a large influence on the sound
For some, winamp 2 may be a better match for its tighter, more dynamic sound, but overall I find that Winamp 5 sound more organic, more fluid, more subtle and more colourful. In short: Winamp 2 may be more precise, but like Foobar, in an already accurate system it may prove too much and overall Winamp 5's smoother presentation may be preferable.
I didn't like Winamp 5 at first instance, due to its dynamic compression. Shame, because otherwise it's very well-behaved, having smoother highs than winamp 2. But it is way too rounded off and lacks dynamics and expressiveness. Please note: this observation was done with standard settings. After some more digging, I managed to find some settings that make a profound difference for the sound quality. If you set them as I will explain below, Winamp 5 will sound a lot livelier while retaining its pleasant smoothness.
1.) plugins - output - select your soundcard or device directly, don't use windows soundmapper, disable volume control.
2.) plugins - input - nullsoft module decoder - enable FIR interpolation (HQ) instead of Interpolation
3.) General prefs - Playback - disable 24bit playback
With these settings winamp 5 loses its "compressed" quality. The feeling that the music was playing with the handbrake on is now almost gone. Everything sounds much faster and more dynamic while maintaining the smoother character Winamp 5 has over winamp 2, which may be drier but is also still more exciting to listen to. Winamp 5 now sounds mature and is an excellent choice if you like some smoothing of your music. Winamp 5 (versioin 5.58) is currently my app of choice.