I faced out with this problem when tried to play Postal 2 on my debian PC. There was no sound and in the console I could see such error:
open /dev/[sound/]dsp: No such file or directory
Google said that aoss from alsa-oss package could help me ... but not on 64 bit system, because Postal 2 is 32 bit app. Ok, 32 bit app should work with 32 bit aoss. And as practice has shown it works. Go to packages.debian.org and download alsa-oss package for i386, then install it with
dpkg -i --force-architecture alsa-oss_VERSION_i386.deb
Now you can start the game with
Notice: this is ugly hack, good practice says that you should make new amd64 package with 32 bit contents with name different from alsa-oss to avoid conflicts with original alsa-oss package.