To use sound on an iMac, disable virtual memory in the MacOS (important).
Make sure you have BootX (1.03b2 or later) installed, with the extension
in your Extensions folder. Start up your computer, and boot Linux via
BootX during startup. This weird method is required because the MacOS
disables the AWACS sound controller if you boot Linux from BootX when the
MacOS has fully loaded (or that's how it was explained to me).
Make sure you have sound support compiled into your kernel. I have 2.2.6
on a rev. A iMac, and sound works fine for me if I follow the above