[NFORCE - NVidia CK8S] ALSA test tone not correctly played back

I have a surround 5.1 playback problem, but stereo playback works:

(1) The sound does not come through continuously, but with crackles and short gaps.

(2) The speaker assignment seems wrong (the center channel of an video DVD can be additionally heard on the left front and left rear).

ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: alsa-base 1.0.22.1+dfsg-0ubuntu3
ProcVersionSignature: Ubuntu 2.6.32-19.28-generic 2.6.32.10+drm33.1
Uname: Linux 2.6.32-19-generic x86_64
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.21.
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC3: privat 1303 F.... pulseaudio
 /dev/snd/controlC0: privat 1303 F.... pulseaudio
 /dev/snd/controlC2: privat 1303 F.... pulseaudio
Card0.Amixer.info:
 Card hw:0 'CK8S'/'NVidia CK8S with ALC850 at irq 20'
   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 0x300, irq 5'
   Mixer name : ''
   Components : ''
   Controls : 0
   Simple ctrls : 0
Card1.Amixer.values:

Card2.Amixer.info:
 Card hw:2 'Bt878'/'Brooktree Bt878 at 0xeeaff000, irq 19'
   Mixer name : 'Bt87x'
   Components : ''
   Controls : 3
   Simple ctrls : 5
Card3.Amixer.info:
 Card hw:3 'U0xeb1a0x2801'/'USB Device 0xeb1a:0x2801 at usb-0000:00:02.2-1, high speed'
   Mixer name : 'USB Mixer'
   Components : 'USBeb1a:2801'
   Controls : 2
   Simple ctrls : 1
Card3.Amixer.values:
 Simple mixer control 'Line',0
   Capabilities: cvolume cvolume-joined cswitch cswitch-joined penum
   Capture channels: Mono
   Limits: Capture 0 - 16
   Mono: Capture 0 [0%] [0.00dB] [on]
Date: Mon Apr 5 19:17:08 2010
InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Alpha amd64 (20100405)
PackageArchitecture: all
ProcEnviron:
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SelectedCard: 0 CK8S NFORCE - NVidia CK8S
SourcePackage: alsa-driver
Symptom: audio
Title: [NFORCE - NVidia CK8S] ALSA test tone not correctly played back
dmi.bios.date: 02/16/2006
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 1011.005
dmi.board.name: 'K8N'
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr1011.005:bd02/16/2006:svnASUSTekComputerInc.:pnK8N:pvrSystemVersion:rvnASUSTeKComputerINC.:rn'K8N':rvrRev1.xx:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.name: K8N
dmi.product.version: System Version
dmi.sys.vendor: ASUSTek Computer Inc.