After skimming through all the comments I did not notice any mention of the interface's OUTPUT level.
The 1st thing I do before recording is arm the track and check it's meter level as I produce the input sound. If it's low I increase the interface's output.
If the mic or instrument is going into a submixer before going into the interface, I will check it's output as well.
Just a side point but, in the real world, you could simply increase the Gain knob at the top of your recording mixer. But Sonar's Gain knob does not work that way.
Steve