I have done a Listening test, all results were graded only by my ears, not any 3rd Party Software (So this Test says nothing about the "real" Quality!)
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Qualitytest of a 192 kbps MP3 file (Lame 3.91 CBR) to best sounding output
192 Kbps beacause of the most used Format I think. B)
All Test with SBAudigy, Driver 324 ripped from Audigy 2 and optical out @ 48khz to a Sony MDSJE530 internal DAC
Headphones used: Phillips SBC HP090 (because Analog out of the Audigy is not god (bad DAC))
POINTS (1 to 10 Points, 1 worst, 10 best)
6 - Windows Media Player (uses Windows intern Frauenhoffer decoder, sounds little better than Winamp but not my Choice

)
5 - Winamp 2.91 Directsound FFHdec (Its ok, but not for me, sounds not so good because of 44khz output, my Card works @ 48khz

)
5 - Winamp 2.91 Directsound MAD 16 bit (little bit dump, no good hights herable, sonds "overdithered", 44khz output...

)
4 - Winamp 2.91 Directsound MAD 24 bit (much more dump, no good sounding at all

)
9 - Foobar 16 Bit out @ 48000 kHz resampled, dither, KS <-- my Favourite, Sounds best for me!
8 - Foobar 24 Bit out @ 48000 kHz resampled, dither, KS
[*] (little bit "different" to 16 bit, more bass, lower hights, could be artefects of truncating)
[*] 24 bit padded to 32 bit
My Settings: DSP: Convert 2 to 4 Channels, Resampler@48000khz fast mode, Advanced Limiter, Replaygain,
Playback: Dither Strong Ath, 16 bit, Kernelstreaming output
This is the best i can get of my MP3s. All the Rest sucks for me, even Winamp with MAD plugin I used for about 2 Jears (!!)
Hope i could help
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To the mods: This Test was only Subjective, don't say me that there is no hearable different between 2 Frauenhoffer decoders, it was only a blind Test and I had chosen!)