I have a question though, what exactly are you seeing from the internal MUC? You didn;t mention an Error message, and to be honest I have not seen the instability that you are talking about. Can you give us a line from your error logs so we can take a look at it. Barring that, here’’;s some information on what to get to install an external MUC.
Well that would depend on the MUC you are using. Lets say mu-conference, download the package, the jcr-runtime, install the dependancies, then install the packages.
You could follow these steps. http://mu-conference.jabberstudio.org/
it is for running with Jabberd2, but with the exception of adding it to external componants in Wildfire, everything still should be the same. After you install it and get it to talk with Wildfire, it should show up as one of the external componants. It is a rather lengthy install, but following the instructions should get you where you want to be.