Taken from the Money's Audio website posted before:
"Monkey's Audio for Apple and Linux is on the way. If you'd like to help, check out the Developers section."
In other words, there is (currently) no way to play .ape files on the Mac. If you have a windows PC, you should be able to use a program to convert the .ape to another format of your choice (for example, 'CDex' should be able to)