I have a SB Audigy, with activated profile 'Output Digital Stereo (IEC958)...' via pavucontrol. If no sound is being played back, pulseaudio switches the digital out off (I can see that on my external amp, which then says 'NO AUDIO' and mutes the channels). If something is played back, PA switches the digital out on (external amp detects this, and unmutes; takes about one second). This leads to a situation where the first second of a song can simply not be heard. If i stop playback, PA switches the digital out off again after a few seconds. This is really annoying. This profile should let the digital out signal on indefinitely (like the underlying alsa does if one enables digital out).
This is not a bug in PA. If at all in your audio equipment. To save power we have to close the audio devices when we are idle. As a workaround you can comment loading of "module-suspend-on-idle" in /ect/pulse/default.pa which will make sure that the audio devices are constantly kept open. This will burn needless CPU time and power but will output a constant PCM stream on your SPDIF at all times.