Optical or coax?

Are you talking about real glass fiber optical (AT&T ST) or plastic* optical (Toslink)?

* Toslink is available now made w/ glass fiber, but still has the same limitations as the plastic stuff.

I would be using a "quality" glass fiber that could be used with the optical output of the mc 861.

OK, if you are referring to the Mcintosh MC861 DVD player, I would definitely recommend using a high quality digital coax. Its "optical" output is Toslink, and although you can get the ICs in glass fiber (as opposed to the standard plastic fiber) it's the transceivers (the thing they plug into on each end) that limit their performance. Also the Toslink cables themselves (glass or plastic) aren't good for much over ten feet if I remember correctly (AT&T can go for miles.) Anyway that's my 2 cents.

My understanding is that if you are coming from a transport that has video capabilities toslink works better. I've tried both in several situations and can't hear any difference. But then, my ears are getting old. (My mind remains firmly planted at about 17 years).