Your dealer should be able to fix it without you having to leave it at the dealer overnight unless it is not a setting problem. But it is a Lexus and you should get treated very well while they are fixing it.
You can also 800-331-4331 (I think?) and they should also be able to fix it for you, unless there is a bigger issue with the stereo.
Call or take it too your dealer tomorrow and if they are unable to resolve the issue call the Lexus customer service.
Even though you did not want the mark levinson, it still should be working correctly. And peace of mind is there isn't a better system in a car from the factory than the Mark Levinson.