Your W220 likely has a COMAND unit, since you're in the U.S. COMANDs don't use a security code (at least, not until the '08 or later model years; I don't know just when they started). You should be fine.
I don't know if it will reset your radio channels, but it is worth a try. You could also try restoring the system to factory presets via the SERV menu, per the instructions in Mercedes Electronics upgrades, installation and retrofits
(sorry, I don't have time to do the search for the specific page right now).