Can the Macs put out 5.1 surround from the TOSlink outputs, or is it just stereo?
All Macs output digital optical. It can be mono, stereo, DPL, DPLII, DD 2.1, 4.1, 5.1, 6.1, 7.1, 9.1 - you get the picture. Whatever is encoded in the medium (e.g., DVD, movie file, etc.), Macs simply passes that digital signal along to your receiver. It does no decoding of the audio file.