problems with playback through mixer
Is anyone else using n-Track alongside the Numark dxm01 usb 24-bit mixer - I can record to n-Track through the mixer (by playing music files from PC through USB cable to the Numark mixer then back to PC) and these playback fine through the soundcard, but when playback is set to the USB Audio device I either get an error opening wav file message or the playback is hopelessly choppy - as I say, playback thorugh the soundcard is fine, so the recording itself is OK - and I can playback from other programs through the USB mixer just fine too - it is ONLY playing back from within n-Track that is being a pain 
I’ve more or less sorted this now, with a combination of advice from Flavio, a download of a Creative Audigy driver update, and by setting Preferences to use both the Audigy AND the USB devices simultaneously.
Hope this is helpful to any other new users working with a USB device.
What I have found when tweaking Preferences is that if you choose a setting which is incompatible with your soundcard setup, the only way of reverting to a working setting is to go back to default settings, close the program, re-open, then reselect the settings which last worked.