Sorry, just saw this thread.
Last night, I logged on to AHIII and vox did not work. When I attempted to transmit, I could see the highlights in the voice box but I could hear nothing, so I tuned to myself and got the same result. Highlight... no sound. (Other game sounds working fine). The game at least knows I'm attempting to transmit.
I've messed with everything, made sure router and PC firewalls are off (made exceptions for AHIII anyway). Rebooted. Uninstalled, downloaded/reinstalled game. Fiddled extensively with SounblasterZ settings as well as Window's sound configurations. Resetv1/2/3 numerous times in game, tried direct tuning to other people. Nothing... I can't hear anyone else, and they can't hear me.
This only happens in Open Melee and Special Events II. All other arena's I could tune to myself and it worked (although, nobody was in any of the other arenas to see if they could hear me).