Were you using ASIO with the US-144? If so, the Conexant does not support ASIO, and will not be an available option.
You may need to rename or delete the audio.ini file.
Change your driver mode in Sonar (Options>Audio>Advanced).
Close and restart Sonar.
Go to Options>Audio>General, and run the Wave Profiler.
Now go to the Drivers Tab. The Conexant should show up.
Check the appropriate I/O boxes.
You may need to restart Sonar for the changes to stick.
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