Tja,

inzwischen weiß ich es. Auf die Frage nach der Möglichkeit per Landweg und welcher Grenzübergang antwortete die Botschaft von Myanmar wie folgt:

To cross the border on the land way you need a special permission. You can apply for this special permission at our Embassy with an English application letter by Deutsche Post (not by Email) mentioning your detailed route, date of arrival and departure at the border checkpoint.
The only possibility to cross the border to Thailand is in Tachilek. It will take two month to get the permission.

Jens