Hardware for 4 or 8 or more inputs to Cubasis

I see that an upcoming new release will support 18 or 24 inputs. What hardware is compatible? Presonus makes a nice 4 and 8 input device. How would I know what will work?

I have an Alesis four channel mixer with firewire out. Is there hardware that would let me use this as an input to the iPad (Cubasis)?