Defaulting to two channels is also the behavior of the downloaded driver from nvidia.
0: nvidia: loading NVIDIA Linux x86 nvidia.o Kernel Module 1.0-4363 Sat Apr 19
17:46:46 PDT 2003
Nvidia + AC97 Audio, version 0.24, 15:22:00 Jul 3 2003
Nvaudio: in Funcction Nvaudio_init_module
PCI: Setting latency timer of device 00:06.0 to 64
Nvaudio: NVIDIA nForce2 Audio found at IO 0xd800 and 0xd400, IRQ 11
Nvaudio: Audio Controller supports 6 channels.
NVaudio: Defaulting to base 2 channel mode.
ac97_codec: AC97 Audio codec, id: ALG32 (ALC650)
Nvaudio: AC'97 codec 0, DAC map configured, total channels = 6
I'm not interested in the Dolby Digital output so much as multiple inputs. BTW, the RealOnePlayer for linux also expects some frequency rate other than the supported 48kHz (if spdif is enabled), so I pass in the spdif_status=0 option when loading the module.