Thema: No AC3 sound on ATV7.3, PCM only

Hi,
I've recently purchased this little box. It came with ATV7.3 preinstalled and there is one big problem - no AC3 sound over HDMI. STB is connected to Pioneer VSX-S520 and feeds only PCM signal, no matter how I set up audio settings I've unchecked AC3 and DTS downmix of course. When I stream the same channel to DreamPlayer on my NVidia Shield TV I get proper Dolby 5.1 sound so this looks like a sound over HDMI handling problem. I can add, that I've asked for help on polish forums and one guy has checked it for me and confirmed, that this problem exists on his soundbar too - PCM only. So it seems that this is not dependent on audio receiver.
Could you help me with this, please?

Thank you for your help. I've installed ServiceApp system plugin from Package Manager without any errors, rebooted, but can't find ServiceApp menu anywhere I've looked in all places found by forum reading and no go. I've even reflashed clean OpenATV image but got the same results HiSlicon service cannot be removed because od dependency. Coul you, please, guide me further how to invoke ServiceApp without visible menu or what to change to mak it visible?

DVB-S2 channels and DVB-T2 channels. Streaming them to DreamPlayer from Zgemma to Nvidia Shield TV yields perfect ac3 sound. So the sources are 100% OK.
BTW: I've just found on https://github.com/oe-mirrors/servic...ugin/plugin.py info when to find ServiceApp menu. It's in Rec/Timeshift not System. So now I can start experimenting with it...