Re: Using optical on a Motu with a Profire
I'm not familiar with any of those boxes but here is a guideline.
If it says Adat (8 channel) optical on both it will work, if it says S/Pdif (2 channel) optical on both it will work. The cable is essentially the same but the format is not.
I have never used T/dif.
Optical connections have a red light coming out of the outputs, but not the inputs. Sorry if that's too obvious. If all else fails then re-boot your interface then your computer & try again, but I never have a problem 'hot-plugging' adat.