Thank you John.All the inputs the interface makes available to CoreAudio should be available to select in the REW soundcard preferences. Difficult to say much more without knowing what interface you are using or what is appearing in the REW soundcard preferences for input devices and inputs.
Yes, that has been my experience also.On Mac, you can only use analog I/O. If you have an audio interface with more than 2 I/O, REW keeps using the 2 first inputs and the 2 first outputs. I have an Apollo from UA and it has 12 analog inputs and 10 analog outputs + 2 ADATs +1 SPDIF but it only works with the first 2 analog I/O whatever you do.
Well, this is how it goes for me at least.