I have a raspberry with 1 USB connected to a USB Soundcard 5.1. The USB soundcard is set as default, and I can play a sound from terminal using MPlayer:
mplayer --channels=6 soundTest.aif
It can be executed in background with this command (not very sure of what it does, a normal & at the end doesnt work):
mplayer --channels=6 soundTest.aif < /dev/null >/dev/null 2>&1 &
If I try to execute this command in two different terminal screens at the same time, the second one doesnt play and basically I have this explanation:
failed (-16): Device or resource busy
How can I play 2 sounds at the same time?
EDIT: Seems to work when using the Raspberry headphones jack