I am currently playing around with the MAM feature and installed the MAM.ixi extension on my node. Unfortunately I ran into an error when trying to access the getMessage function:
"Request Error: TypeError: Transaction.quietFromHash is not a function"
It's caused by the ixi extension, but I'm not really familiar with those extension and not sure if you could debug them. (https://github.com/iotaledger/MAM.ixi/blob/master/index.js, line 22).
I basically used the examples from the github: https://github.com/iotaledger/mam.client.js