Direct optical out of Mac vs USB asynchronous

I suspect Toslink from Mac would definitely benefit from reclocking. Optical is great avoiding ground loops, has no transmission line effects and is immune to ambient electrical noise, but because of slow transitions it suffers from the system noise on the either side (computer or DAC). Since every computer is pretty noisy I would avoid this route without reclocking. Asynchronous USB, when designed right, can be almost perfect - at least in theory.

"I seem to recall that most Mac's let you take a digital stream of sound directly out of one of the jacks (headphone?) with a special connector."

I used the headphone/toslink connection when I used to have a Mac. Given a choice, I would probably just go USB. I didn't like the way the optical connection was set up. I remember me being on the phone arguing with apple telling them it was impossible for a headphone jack to be a toslink as well. I thought it was some kind of misprint, but I was proven wrong. You get this little adaptor and on one side of it, the toslink cable plugs in, and the other end is a mini headphone jack with a little hole at the end of it for the light to go through. When I first saw it, I couldn't stop laughing. It was a cheesy setup, but it was a pretty cleaver idea.

"Does direct digital also need reclocking?"

Not sure what you mean. USB or Optical is digital. Generally speaking, reclocking is almost always a good idea. Especially if you are using entry level equipment.

Art - my iMac can only play 24/96 via optical - that's why I use USB - I required 24/192

Granted USB can be a PITA, but once you overcome it's "shortcomings" it can play higher resolution files.

Take a look at the following thread for one of many cabling/power solutions

Do You Use USB for Streaming?

Regards