I just got a Lexicon Alpha usb audio interface, but it's not showing up as a usb device or as a sound card.
Try unplugging the USB cable and plugging it back in. This might trigger detection.
I have Lexicon Alpha with Kubuntu system (and Win7 dual boot). Linux and Windows does not detect the stupid sound card on login, I must manually unplug the USB cable and plug it again to detect the card, everytime!