Optical digital ( or coaxial ) is still the preferred digital connection for high end 2 channel ! I only know of one quality DAC that uses HDMI ( NAD 51 ) and that is more of an additional feature as it still runs optical and coaxial.
HDMI is notably worse for jitter that optical and is not in any way a better connection for music.
For the cost of a few cents in production Apple have lost and entire, but small market, those who use external DAC's or DAC equiped 2 channel amplifiers.
Adapters, as posted are a pain and typically made of cheap components and sound poor.
Those saying that optical is old tech are demonstrating a very incomplete knowledge of the audio world.
There are / was a reasonable group of "audio" guys hoping that this ATV would have HiRes, 24bit, audio, and that apple might enter that area perhaps with a higher fee as some others have done, seems that instead they had gone backwards.