Actually, thats not quite true. HDMI has the ability send 8 channels of uncompressed bit-streamed audio to a receiver or other device. Optical audio only has the capacity for 2 channels of uncompressed audio... now, wait wait, what about Dolby Digital 5.1? Well thats a compressed audio package, and optical has been updated to accommodate it, but HDMI has the capacity to carry higher resolution audio signals. In regards to the ATV, to my knowledge, DD 5.1 is the highest resolution surround format supported, but I could be wrong. However, lets be clear that while the ATV will send the same data over HDMI and optical, with its current software, the HDMI port has the capability to pass much higher resolution audio - which could come in the form of a software update sometime in the future...