I installed this on my old QuickSilver G4 933 running Mac OS X 10.5.6 and it works and sounds excellent. I have an M-Audio Revolution 7.1 audio card and an older set of Klipsch 5.1 speakers with a dual 6" speaker powered sub woofer. The sound is amazing. It also plays out through my Kenwood 5.1 home theater system through the digital output from the sound card or through my XiTEL Pro HI-FI Link USB audio breakout box. Output through headphones is also much improved over standard stereo files. I downloaded all the free MP3-5.1 samples from all4mp3.com. Although the music is not all my style it does show off all of the great qualities of this player and these specially encoded files. I have yet to try the encoder. I hope it works as well as the player does.
The only thing lacking is a streaming browser plugin for Mac web browsers. I also hope this is something they will offer in the future.
I am very impressed.