Don't have the USB series but I have the new ZED R16 Firewire desk which does what you're asking for and more.
My understanding is that the cheaper USB Series models will only feed the master bus output to a DAW and not individual tracks to separate tracks in a DAW.
The R16 is a great analog mixing desk combined with a FW audio interface.
Here's my ZED R16 which will have to make do with sitting on my rack until I move back to Oz and get another desk:
Yep, the USB series only feeds the Main LR output, not the individual channels. If you want a mixer that sends out individual channels you shold have a look at:
Phonic Helix Board
Alesis Multimix Firewire
Mackie Onyx Firewire
Yamaha N Series
Allen & Heath ZED R16
I really fancy one of the ZED R mixers myself, just dont have £1500 lying around unfortunatley