I have had Sonar X2 working with an Omega happily (although it is not the fastest interace in the world). As suggested, best download the latest drivers. Your post suggests Sonar is not seeing the correct Lexicon inputs as mine says lexicon omega not just usb 1 and 2. There are things you need to do in device manager to disable the non ASIO/USB  inputs there is stuff on the web about this.