Thanks for your response Michael. Unfortunately neither of the two people I'm trying to help, get it to work: it doesn't show up in the evaluation engine window, nor is it available as a game variation under Preferences.
One of them mentioned his MacOS 10.9 is actually called Maverick; 10.8 is Lion. Maybe that has something to do with it? It's also on 64-bit systems, for the record.
Anyhow, thanks for the help, I hope we somehow get it to work and I'll report back. I had no problem using hypergammon on Windows7-64bit, one just needs administrator rights to move the file to Program Files (x86)/gnubg.
Since I've been playing hypergammon in matchplay, I realised normal backgammon match equity tables will be off by a fair margin probably, because of the much higher gammon and backgammon rates in hypergammon. So I'm experimenting with building a special hyper3.met, which so far indeed is quite different from ordinary METs. If I reach some further progress on it, I'll post a version of it. Is anyone aware of an existing MET for hyper matches? I couldn't find one on a quick search.