Anthem is still a work in progress, and so should be currently viewed as such. Features are being added at a very fast rate. Have a look at the main page for a pretty accurate list of current Anthem features. I don't know. If anyone knows of a good audio engine that can be 'plugged in' then I'm very willing to find out.
Anthem is portable.
As long as your Unix platform supports KDE2, the Anthem interface will run on it. As long as the TSE3 library supports your platform's soundcard, you can have sound. You're welcome to help port it, though. You will need a fairly recent KDE2 snapshot, and the TSE3 library. Full instructions are contained in the source package.