pulseaudio cracking noise with digial audio IEC958 5.1

[manwe_]

Hi *.

I'm switching from Logitech Z-10 stereo speakers to Logitech Z906 (5.1 surround), but having trouble with pulseaudio. Sound card is USB SoundBlaster X4. When connected via 3 jack cables (5.1 analog output) - works fine. Same with digital optic cable (IEC958) in stereo mode. But as soon as I switch from digital stereo (IEC958) to digital surround 5.1 (IEC958) all speakers start to emit cracking noise, even when nothing is playing.

Tested on Windows, no problems there. For now I can stay on analog 5.1 but would really like to switch to digital.

Any ideas?