[nst7]

As far as I can see, this won't work. Neither unit functions as a standalone converter, which is what you would need them to be to use the way you're describing.

Very few low budget interfaces have that capability. In the future, you will probably want to find out if it does what you need before buying.

I don't know if it's possible for you to return it.

You will want to get a unit like the ART Digital MPA or DPS.

Or, even better, buy one interface that has all the inputs that you need. In the long run that will be cheaper. Something like the new Focusrite Scarlett 18i8 or 18i20 would be great.

But they won't work with Protools Express, if that's what you have. You will need the full version of Protools.