I use a Mobile PreUSB which I’m pretty sure does the same thing.
What I do is capture the audio first with Audition, do some editing and then import it into Premiere.
You can record directly into Premiere with the audio Mixer, but then editing would be very tough.
If you put two channels into your USB device, they will be mixed together into one channel.
You can buy a Mackie firewire mixer and it will give you discreet channels of audio, but it’s about $600.