Now that I think of it, I seem to recall that the Impact worked as a MIDI controller right away when I first plugged it in. This is the way any MIDI controller would work, I think: If the OS recognizes it, so should SONAR. The link I gave you is mostly to get the DAW controller functions working. Therefore my new advice to the OP is to follow Keni's advice above.
PS: You can now get the Bandlab version of SONAR Platinum for free. You should consider it.