On the raspberry pi, using the internal sound card by default you can output audio from multiple programs simultaneously and it mixes them together.
Since switching to a USB soundcard (merely by commenting out the line "options snd-usb-audio index=-2") in /etc/modprobe.d/alsa-base.conf, I can play audio and control volumes perfectly well, but cannot play simultaneously from multiple programs.
After starting one (and getting audio out) and then starting another, I get "audio open error: Device or resource busy"
Is there a way to re-enable this functionality? I am using a Griffin iMic USB sound card.