Here is my alsa config : http://www.alsa-project.org/db/?f=d8c96ba81442526650f277e0b7d43dfb6fd668a4
On raspberry I cannot use dmix plugin, when I run a speaker-test with a very simple config using dmix (refer given config in alsa result), its stays stuck. When I use default alsa config (direct use of hw:0,0 without dmix), mixing is done as said here :
NOTE: For ALSA 1.0.9rc2 and higher you don't need to setup dmix for analogue output. Dmix is enabled by default for soundcards which don't support hardware mixing. You still need to set it up for digital outputs.
Here are some users having same problem http://raspberrypi.stackexchange.com/questions/57787/using-the-alsa-dmix-plu... . I'm not sure it is an alsa problem. But alsa developers could help solving this issue.
regards lah