Certainly possible, but as pointed out, why would you need the mixer? You can do ten channels at a time on the Firepod (8 analog and the last 2 would be a stereo S/PDIF single input). Are you wanting to get more stuff going into a mixer (more the eight/ten channels), then have the mixer mains go into two of the Firepods channels? No matter what you do, the Firepod has a max of ten inputs at one time and unless you have a decent mixer, you'd be introducing something to the signal chain that doesn't need to be there.
P.S. Welcome to the board, but please try not to crosspost the same question in multiple categories (I see you posted this in the newbie category as well). One or the other would have been just fine.