You absolutely can do that. If you're working on a Mac you can create an "Aggregate Device" that include multiple audio interfaces. Then select the aggregate device in your DAW of choice and you can use all of the inputs.
Alternatively, I presume you could also ADAT to link the two together.
I've actually been looking at doing something similar so I have more line level I/O for outboard effects units and instruments. Let me know how it's going!