I've recently bought a new PC, installed Ubuntu and am now unable to get 5.1 digital sound working. Simple analogue stereo works fine on both the front and rear connectors.

On my old box I connected the coax connection from my soundcard to my surround sound amplifier, set Settings->Sound to "Digital Stereo Duplex" and it worked.

My old soundcard doesn't fit in my new machine so I'm using the built-in sound hardware. I'm connecting the combination output socket on the back of the PC via the same cable to my surround amp as before.

The MB is an MSI Global H61M-P31 with an RealTek ALC887 sound chip.

When I go to Settings->Sound I only see "Headphone Built-in Audio" and "Analogue Output Built-in Audio" - no digitial options.

The output from aplay -l is:

default
Playback/recording through the PulseAudio sound server
sysdefault:CARD=PCH
HDA Intel PCH, ALC887-VD Analog
Default Audio Device
front:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
Front speakers
surround40:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
4.0 Surround output to Front and Rear speakers
surround41:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
dmix:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
Direct sample mixing device
dsnoop:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
Direct sample snooping device
hw:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
Direct hardware device without any conversions
plughw:CARD=PCH,DEV=0
HDA Intel PCH, ALC887-VD Analog
Hardware device with all software conversions

While googling for ALC887 I've seen some references to "ALC887 -VD Analog" and some to "ALC887 -VD Digital". Does anyone know if I need to force it to chance mode somehow?

It's worth mentioning that when I set the output to 5.1 digital surround in Windows 7 on the same machine I still don't get any sound so it's not a unique Linux problem.

Thanks for any help.