I used Altis Altima optical until my system got good enough to let me hear, very clearly, the superiority of S/PDIF coaxial or AES/EBU. Mgl123's comment on the literature also squares with my experience. I've heard that the signal has to be converted twice, with optical, since it starts out, and must end up, electrical. I hope I have that right, but don't bet the farm on it. Anyway, I'd avoid optical.