UPDATE: Drivers have been added by Avid with support for 10.9.1. Please go to www.avid.com/drivers to download the latest driver for your interface.
Please Note : Mac OS X 10.9.1 Mavericks is NOT approved at this time and should not be used until Avid announces support for it. Attempting to use Mac OS X 10.9.1 with several Fast Track Models ( Pro, Ultra C400, C600 for example) with the approved Mac OS X 10.9 Maverick driver(s) will result in No Sound out.
For more information, see this article from Avid’s knowledge base.