The grayed out 24-bit or whatever is not where you change the record bit-depth.
You go to Preferences, then File, Audio Data (I am doing this from memory so please forgive me as I am not at my own computer at the moment).
It might be under Project somewhere too - someone else, please feel free to correct my old-farty brain.
Anyways that is where you change the default record bit-depth for new projects.
Your sample rate must match between Sonar and your interface settings. For a starting point, try 24-bit recording at 44100 sample rate, and an ASIO buffer size of 128, and see what happens.
Please note that it is recommended that you cycle your interface after making the settings changes. This can be unplugged or powered off/on, either way is fine.
Sorry for any mistakes in the precise location of that, but it is there somewhere near there.
Bob Bone