Hdmi is great for ht and multichannel applications, but I wouldn't use it for a 2 channel music setup. Some dacs use an hdmi connection for i2s, but that is different than your standard hdmi on a processor/receiver.
On The Mac, I would look into a USB to spdif converter which sounds better than the optical output in my experience. Even the inexpensive hiface sounds better than a glass mini toslink from my Mac mini.
