[Darryl Ramm]

You can't "take advantage of" the preamps in the Apollo, well not via ADAT, since it only has ADAT input, it's not intended to be an ADAT preamp.

So you want to do ADAT input and output via the Focusrite. Get one thing at a time working and make sure the focusrite is set up to talk ADAT not S/PDIF

Since you are not using the Focusrite as a interface you have to set it up in stand-alone/mixer mode to tell it what signals to send/receive from the ADAT connections. All described very well in the documentation.

I would focus first on getting the Focusrite to run as an ADAT mic preamp, then worry about additional outputs for headphones.

And if still stuck... post a screenshot of the relevant IO pages in Pro Tools.