Did you instaled the latest driver ver. 1.70? Remove (uninstall) your driver, unplug the USB cable, reboot your system then install the latest driver with your USB Cable unplugged. then plug your mixer and open the mixer driver software, then select "rec out" on one of the 4 stereo channels on the mixer output tab. On the other 3 output channels you can select "none". On your prefered software select the channel and it should work!
Sorry for the poor english - im from Brazil!