bobby@bobby-ubuntu:~$ aplay -L |grep surr  #look for surround51 'cards.pcm.surround51'
surround40 'cards.pcm.surround40'
surround41 'cards.pcm.surround41'
surround50 'cards.pcm.surround50'
surround51 'cards.pcm.surround51'
surround71 'cards.pcm.surround71'
bobby@bobby-ubuntu:~$