More details about what "doesn't work" means would be helpful. Do you
see a SPDIF option in the sound output settings?
In "pavucontrol", it actually does have a listing for the Xonar Sound Card, but only the analog output port is available. In alsamixer, I can press F6 to select sound card, and "Xonar Sound Card" is a selection, but there is no iec958 device.
[mythtv@seveneves ~]$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: SoundCard [Xonar SoundCard], device 0: USB Audio [USB Audio]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 0: SoundCard [Xonar SoundCard], device 1: USB Audio [USB Audio #1]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: SoundCard [Xonar SoundCard], device 2: USB Audio [USB Audio #2]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: SoundCard [Xonar SoundCard], device 3: USB Audio [USB Audio #3]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: PCH [HDA Intel PCH], device 0: ALCS1200A Analog [ALCS1200A Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 1: PCH [HDA Intel PCH], device 7: HDMI 1 [HDMI 1]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: PCH [HDA Intel PCH], device 8: HDMI 2 [HDMI 2]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: PCH [HDA Intel PCH], device 9: HDMI 3 [HDMI 3]
Subdevices: 1/1
Subdevice #0: subdevice #0
[mythtv@seveneves ~]$ lsusb
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 002: ID 0b05:189d ASUSTek Computer, Inc. Xonar SoundCard
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 002: ID 051d:0002 American Power Conversion Uninterruptible Power Supply
Bus 001 Device 006: ID 0a5c:21e8 Broadcom Corp. BCM20702A0 Bluetooth 4.0
Bus 001 Device 005: ID 05e3:0610 Genesys Logic, Inc. 4-port hub
Bus 001 Device 008: ID 046d:c001 Logitech, Inc. N48/M-BB48/M-UK96A [FirstMouse Plus]
Bus 001 Device 003: ID 26ce:01a2 ASRock LED Controller
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
But it actually is a PCIe x1 card.
If I get into the audio settings in MythTV, it will show the iec958 device, but setting the audio to use it produces no sound.
That is really old information. Probably the reason it's hard to find
anything more recent is because generally it all just works.
That's true for stereo sound, but not so true when you try to use surround sound and iec958 devices.
--Greg