Optical audio out on nForce2

[l0b0]

I've tried for some days now to get an optical signal (S/PDIF, aka. IEC-958 type II) from my Nvidia nForce2 onboard audio chip to my Logitech Z-680 5.1 surround system, without success. I've checked the User's Guide, man pages, and forums for help.

Installation information:
FreeBSD 6.2-RELEASE (last

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portsnap update && portupgrade -a

today)
Installed the kernel sources with sysinstall, then installed OSS 4.0.b1003_1:

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cd /usr/ports/audio/oss/ && make install clean

Ran ossdetect.
I have not added any sound settings to /etc/sysctl.conf.

The result so far:

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$ cat /usr/local/lib/oss/etc/installed_drivers
ich #Nvidia nForce2
vmix #OSS Transparent Virtual Mixing Architecture

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$ sudo ossinfo
OSS has not detected any supported sound hardware in your system.

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$ ls /dev/dsp*
/dev/dsp0.0   /dev/dsp0.1   /dev/dspW0.0  /dev/dspW0.1  /dev/dspr0.1

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$ dmesg | grep pcm
pcm0: <nVidia> port 0xd000-0xd0ff,0xd400-0xd47f mem 0xd5080000-0xd5080fff irq 22 at device 6.0 on pci0
pcm0: <Avance>

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$ sysctl hw.snd
hw.snd.targetirqrate: 32
hw.snd.report_soft_formats: 1
hw.snd.verbose: 1
hw.snd.unit: 0
hw.snd.maxautovchans: 0
hw.snd.pcm0.buffersize: 16384
hw.snd.pcm0.vchans: 0
hw.snd.pcm0.ac97rate: 48000

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$ cat /dev/sndstat
FreeBSD Audio Driver (newpcm)
Installed devices:
pcm0: <nVidia> at io 0xd000, 0xd400 irq 22 bufsz 16384  (1p/1r/0v channels duplex default)

What have I done wrong? I can't find any howto for installing and configuring OSS. I don't know which parameters to use for e.g. VLC - I've tried anything I could think of (I've set "Use S/PDIF when available", and tried setting the device to /dev/dsp, /dev/dsp0, /dev/dsp0.0, and /dev/dsp0.1). The Logitech control center just shows "Detecting..." when the input channel is set to optical.