One more thing, the optical cable can only handle Dolby Digital as a multi-channel spec. A better argument for going 2.1, since you can only stream 2 channels as uncompressed audio. You could use the analog outputs, but they are going to be pretty lousy as far as noise goes.
I would just run the optical or USB out to a DAC, and the DAC out to a couple of good powered monitors and maybe a subwoofer.