I recommend you set SONAR to use the M-Audio interface and monitors, and have Windows, browsers and other generic multimedia apps use your onboard sound, either through a separate set of speakers or connecting to the same monitors via an external mixer. This keeps Windows from messing with your audio interface, and causing problems for SONAR, and vice versa.
- Under Preferences > Audio > Playback and Recording, set the Driver Mode to ASIO.
- On the Devices page, check the I/O ports for the Fastrack (you shouldn't even see soundcard ports here).
- On the Driver Settings page, make sure the Playback and Record Timing Masters are both referencing channels of the Fastrack.
- Under Sound in the Windows Control Panel, set the Default Devices for Recording and Playback to the soundcard I/O.
The MIDI setup shouldn't have any bearing on how audio works, but if there's any problem using MIDI in SONAR, that can be addressed separately.