We get this question a lot. Seems that there are many long time craft beer lovers out there who have had kegerators for a long time with commercial connections. Now, with the growth of homebrewing, these long time craft beer lovers and kegerator owners are finding themselves in a sitution with soda kegs which have different fittings.
Connecting a soda keg directly to a commercial keg coupler cannot be done. However, the commercial coupler can be modified to allow it to fit ball lock or pin lock disconnects (as well as the sanke/commercial connection). In order to connect a soda keg (ball lock or pin lock) to a commercial keg copuler, you'll need a commercial to homebrew conversion kit. Disconnecting the lines from the sanke/commercial connection, you'll attach the barbs to the beer lines and the MFL tailpieces to your sanke coupler. This will give you threaded connections that can now be used to switch your existing beer lines to/from soda kegs to commercial kegs and vice versa. All you'll need on the other end is the appropriate threaded corny keg disconnects.