I'm having some problems with volume levels switching between sources. I have several different HDMI sources connected to my HD621. Most work fine, except for my cable TV STB. Unlike my PS4, Bluray etc. the STB only has the option of stereo or 5.1 DD under audio output.

This still works fine when watching a TV channel that actually transmits multichannel audio. But on stereo channels the volume is extremely low. If I turn the G68 volume to max normal speech can be heard OK, but that's about it. If I change channel without minding the volume I can blow the roof off the building...

I've tried with different cables and with different STBs with no change. So I'm pretty sure the problem is either with the HD621 or the G68.

Any one experienced something similar? All suggestions on troubleshooting this is appreciated.