For those that can't seem to get their audio level high enough on their Mac, a recent submission to the mactel-linux-users list may have revealed the solution.
NOTE: Before using the following, first, run 'alsamixer' in a terminal and make sure that all your channels are unmuted (m-key) and turned up (arrow-keys). After you have tried everything in alsamixer (including switches) then try the below.
Well, guess what, Hardy uses pulseaudio. So to check the volume level in pulseaudio run:
Originally Posted by mactel-linux-users
and look in the "Output Devices" tab. You should be able to increase the pulseaudio mixer controls there.
If you want to play with paman, you have to install it.
After that, you can run and look on the "Devices" tab. You can select the "alsa_output" device under "Sinks" and click properties. Here you should be able to increase the level of the output device (Maybe even past 100% so be careful!).
sudo apt-get install paman