Hi. I may be wrong but I'm pretty sure you can't use 2 interfaces at the same time. What you need, as far as I know, is an interface, such as the 1824c, plus a mic pre-amp unit such as the Presonus Digimax D8 or the ********* ADA8200. You connect the interface to the computer via USB and the pre-amp to the interface via ADAT. By the way, I have an 1818VSL combined with an ADA8200 set up in this manner. I hope, though, that connecting the 2 interfaces is possible... good luck.