In order to have voice support in aMSN (http://www.amsn-project.net/) a third party library named libsnack is required. Some distributions have this library in the repositories while some do not.
The snack libraries are available at http://www.speech.kth.se/snack/download.html. If you can't find the binaries for your distro, download the source and compile.
tar xvf snack2.2.10.tar.gz
sudo yum install tcl-devel tk-devel
sudo make install
If snack is already installed but aMSN reports that it cannot find the libraries. The solution is listed here http://www.amsn-project.net/forums/viewtopic.php?t=4969&highlight=snack. In my system, snack was installed in /lib/snack2.2 and it wasn't included in the aMSN path. To figure out the path used by aMSN, load aMSN and press Shift+Ctrl+C to bring up a console. Then type set ::auto_path If /lib is not in the output, create a symlink to /lib/snack2.2 in one of the paths searched by aMSN. I simply did
sudo ln -s /lib/snack2.2/ /usr/share/tk8.5/snack2.2
Now aMSN should detect libsnack and audio settings should work as expected.