Earlier I posted a dirty hack how to get the sound going again with flash on 64bits.
Now we have www-plugins/adobe-flash-10.1.53.64-r11 in the repositories with a cure for that.
If you did follow my previous post on how to get it working with mozilla-firefox, you should undo that (remove the libflashplayer.so from ~/.mozilla/plugins )
equo update && equo install www-plugins/adobe-flash-10.1.53.64-r11
Now you should check if you have /etc/asound.conf with the following contents:
Reboot and all should be fine again.