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Adapters are not the solution - this was provided to me by Sennheiser's Technical Director in the US:

"Upon further analysis, even unbalancing will most likely NOT work, as tip and ring are...

We chased down that answer in this thread:

http://www.reduser.net/forum/showthread.php?81966-Sennheiser-MKE-400

First, we started on the connectors - which seemed to be the right ones.
After...