First, let's start with something fun.
Have you perhaps activated unlimited limiting?
OK, real life.
I'm assuming that you've installed the Focusrite ASIO driver. Have you enabled it for use in SONAR via Edit | Preferences under Audio | Devices, Audio | Driver Settings, and Audio | Playback and Recording? If so, what track(s) and type(s) (audio, MIDI) have you created? What do you have (instrument(s) and/or mics) plugged into the Focusrite? Do you have monitoring enabled on the track(s)?
Sorry for all the questions. I have more, but will stop here.