[NFORCE - NVidia CK804] ALSA test tone not correctly played back

I cannot get any sound on Ubuntu 10.04, but I haven't tested previous versions.

I have tried a lot of combinations of settings using alsamixer, but nothing works. Some people on the web say I have to mute the SP/DIF output, which didn't have any effect. I'm at a loss what I can do now.

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: alsa-base 1.0.22.1+dfsg-0ubuntu3
ProcVersionSignature: Ubuntu 2.6.32-24.43-generic 2.6.32.15+drm33.5
Uname: Linux 2.6.32-24-generic i686
NonfreeKernelModules: nvidia
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.21.
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: joris 1396 F.... pulseaudio
 /dev/snd/pcmC0D0p: joris 1396 F...m pulseaudio
Card0.Amixer.info:
 Card hw:0 'CK804'/'NVidia CK804 with ALC850 at irq 22'
   Mixer name : 'Realtek ALC850 rev 0'
   Components : 'AC97a:414c4790'
   Controls : 42
   Simple ctrls : 27
Card1.Amixer.info:
 Card hw:1 'UART'/'MPU-401 UART at 0x330, irq 10'
   Mixer name : ''
   Components : ''
   Controls : 0
   Simple ctrls : 0
Card1.Amixer.values:

CurrentDmesg:
 [ 33.592011] eth0: no IPv6 routers present
 [ 86.080028] Clocksource tsc unstable (delta = -291692776 ns)
Date: Sun Sep 26 12:31:45 2010
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release i386 (20100427.1)
PackageArchitecture: all
ProcEnviron:
 LANG=en_US.utf8
 SHELL=/bin/bash
SelectedCard: 0 CK804 NFORCE - NVidia CK804
SourcePackage: alsa-driver
Symptom: audio
Title: [NFORCE - NVidia CK804] ALSA test tone not correctly played back
dmi.bios.date: 11/25/2005
dmi.bios.vendor: Phoenix Technologies, LTD
dmi.bios.version: ASUS A8N-SLI ACPI BIOS Revision 1014
dmi.board.name: A8N-SLI
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: 1.XX
dmi.chassis.asset.tag: 123456789000
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnPhoenixTechnologies,LTD:bvrASUSA8N-SLIACPIBIOSRevision1014:bd11/25/2005:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnA8N-SLI:rvr1.XX:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.name: System Product Name
dmi.product.version: System Version
dmi.sys.vendor: System manufacturer