In /etc/dosemu/dosemu.conf, I add the line "$_sound =(2)". This enables experimental sdl sound. But in this case, minimal sdl provided by dosemu is not sufficient. If you want to hear something from the speaker, you must emerge media-libs/libsdl.
Starting from dosemu-1.4.1_pre20130107 media-libs/libsdl is a required depend for dosemu in gentoo. Once upstream moves ot to user-switchable --enable-/--disable-sdl we'll add it under 'use sdl'. Thanks for report!