You do not need to change trains to get from the Le Meridien Munich to the airport. Just get on the S1 or S8 at the Hbf.
Unfortunately there are works being done on the track and on Saturday evening, when we tried to take the S bahn to Ostbanhof, there were no trains and you had to go to Odeonplatz and change to replacement buses. This is temporary I am sure but it would have required additional time and changes to make our way to Ostbanhof to take the train to the airport. So currently, no direct train at some time of the day (evening, night and week end)