SPDIF output always on? or never?

[FelixC]

My motherboard supports 6-channel analog and digital sound using the
Realtek ALC655 chip. The digital output is SPDIF, and I have both
optical (TOSlink) and electrical (RCA) output connectors. I've never
used them, but I'm thinking of hooking up a Creative Labs 5500D
speaker system which supports digital input.

My ignorant question: what sound signal (if any) normally comes out of
the SPDIF output? Does it normally output a PCM version of the
2-channel sound coming out of the analog stereo outputs? On the
Realtek control panel the only relevant item I see is a checkbox which
says "SPDIF only", which I think implies that sound normally comes out
of both analog and digital outputs unless this is selected.

I think I understand correctly that it *should* be able to output the
AC3 Dolby Digital sound track played from a DVD, but does it need to
be enabled in some way? Is it automatically supported by DVD player
software?

I think I also understand correctly that the computer doesn't have
enough hardware or software computing power to encode a real-time
Dolby Digital signal from 6 discrete channels. I assume therefore that
the only way to get 6-channel sound from games or other sources which
aren't already encoded is via the analog outputs?

 

[FelixC]

My motherboard supports 6-channel analog and digital sound using the
Realtek ALC655 chip. .....
My ignorant question: what sound signal (if any) normally comes out of
the SPDIF output? Does it normally output a PCM version of the
2-channel sound coming out of the analog stereo outputs? On the
Realtek control panel the only relevant item I see is a checkbox which
says "SPDIF only", which I think implies that sound normally comes out
of both analog and digital outputs unless this is selected.

Answering my own question after experimenting with an outboard digital
decoder:

The digital audio output from the ALC655 on the motherboard is "always
on", at least on my system. The various check boxes don't seem to
affect it at all. The equalizer controls in the Realtek driver also
don't affect the digital sound output - only the analog. There's no
significant difference in quality between the analog and digital
outputs, putting aside the controllable volume and equalizer settings
possible on analog.