Jeff K. has a bone to pick with Apple:
I have a great set of speakers that I connected to my old iMac with a optical audio/mini-plug cable through the headphone jack. They had terrific sound. Imagine my surprise then when I connected the cable to the headphone jack on my new iMac and it wasn’t recognized. I called Apple, and it turns out someone decided to change that part of the audio electronics. No more digital optical. My speakers already have a DAC [digital-to-analog converter] built in, so it’s not a matter of adding one.
Starting in 2006, Apple incorporated support for S/PDIF, an optical digital connection standard that uses a fiber-optic cable with a Toslink connector or through Mini Toslink, which is compatible with standard 3.5mm audio jacks. This allowed higher-quality digital audio output, and this standard allows for 5.1 and 7.1 surround sound encoding, depending on the source device.