As I said in this thread, I do not know if the reason why those options are blank in kxmixer is due to a bug, or if it is because those options are not currently supported on that OS, but, all of those settings can be changed in kX Console (assuming that they are in fact supported, and that the bug (if it is a bug) is only with the GUI).
To enable AC3 Passthru, type the following in kX ...



