What Mac Model do you currently have? Many of the Macs can output dolby surround via their audio output jack. Just plug in a toslink optical cable or a typical optical cable with an adapter to make fit in.
http://www.google.com/search?client...YQrQQwAg&biw=1095&bih=727&fp=f478bdfafcb0c911
I am sure that Macs do playback the dolby surround sound from a DVD using the DVD player and you can get the dolby surround audio via the toslink/optical audio out.
I am not sure about iTunes. Other MR members can help with that.
The music that you have in loseless is also in dolby surround?
Please correct me if I am wrong, but most of the music is recorded in stereo, some were in Quadraphonic, and a very few SuperAudio CD actually play very well in a surround sound home theater.