Comment 16 for bug 1051665

http://ubuntuforums.org/showpost.php?p=9385594&postcount=4

may be device 1 is also used for spdif on you x-fi pro,

so you need to define the device of iec958 and you have to send email to <email address hidden> about the name "Pro" or "SB X-Fi" or " SB X-Fi Surround 5.1 Pro"

card 1: Pro [SB X-Fi Surround 5.1 Pro], device 1: USB Audio [USB Audio #1]
  Subdevices: 1/1

!-------Mixer controls for card 1 [Pro]

Card hw:1 'Pro'/'Creative Technology Ltd SB X-Fi Surround 5.1 Pro at usb-0000:0b:00.0-1, full sp'
  Mixer name : 'USB Mixer'
  Components : 'USB041e:30df'
  Controls : 1
  Simple ctrls : 1
Simple mixer control 'Power LED',0
  Capabilities: pswitch pswitch-joined penum
  Playback channels: Mono
  Mono: Playback [on]

# If a device does not use the first PCM device for digital data, the device
# number for the iec958 device can be changed here.
USB-Audio.pcm.iec958_device {
 # "NoiseBlaster 3000" 42
+ "SB X-Fi" 1
+ "Pro" 1

 # The below don't have digital in/out, so prevent them from being opened.
 "Blue Snowball" 999
 "Logitech Speaker Lapdesk N700" 999
 "Logitech USB Headset" 999
 "Logitech Wireless Headset" 999
 "Plantronics GameCom 780" 999
 "Plantronics USB Headset" 999
 "Plantronics Wireless Audio" 999
 "SB WoW Headset" 999
 "Sennheiser USB headset" 999
 "USB Device 0x46d:0x992" 999
}