DLSMusicDevice is a built-in AU SoundFont player for the Mac OS. It's listed under the Apple Audio Units.

Download some SoundFonts (piano is default) here:
* Sf2midi.com * Free Soundfonts * SoundFonts.it

Once you have your SoundFonts, place them in the following path:

HD/Library/Audio/Sounds/Banks/

If you happen to download any compressed SoundFonts (sfArk) files, you can decompress them with sfArk.