The new Media Player has an equalizer that works very well so I don't see how any other player could sound better.
Assuming identical hardware and no equalizer adjustments, I would think there are better or worse ways to turn some ones and zeros into musical notes, and then better or worse ways to "handle" those notes.
Just like anything else we do on our computers... better or worse ways to compress, copy, sort, search, etc.
And I think that the player we use has an effect on these sounds as well.
Our ears "hear" in analog. Music is mostly recorded in analog as well.
In between, our computers, can only do... "digital".
Depending on the actual source (analog or digital), the music has to be converted at least once, and maybe twice.
When converting from analog to digital and back again, certain assumptions (like... rounding off), are made.
These conversion(s) necessarily destroy or add to the source (making assumptions based on code).
These conversions are done mostly in the hardware. But then the player, receiving these signals from the hardware,
has it's own effect on the sounds, determined mostly, by the quality of the coding of the player itself.
That's what I meant when I said that some players, "sound better" than others.
After all, a player is just another piece of software between the source and the listener.
Now cue the emcee to announce the "tubes versus IC chips", debate. :)