It's just a player, and no, it doesn't use WMP to play.
The main reason for it being ported was that you need it to access Apples (until today) mac only iTunes music store, which allows you to buy then download music. Before that it had just always been the macs default mp3 player.
Well now we get to play too
Ok, just downloaded and installed...and I have to say, I'm very impressed.
I've been comparing sound quality between WMP9 with the DFX plugin enabled, and iTunes with the built-in Sound Enhancer turned on, and the sound quality is the same, if not better, in iTunes, even though it isn't using any external plugins.
It's also nice to see the built-in mp3, AAC, WAV and AIFF encoders.
I think I'm going to finally switch over from WMP9.