I received my Sig 30 minutes ago.
The volume control acts completely normal.
Clicks on and both channels rise from zero volume both in balance throughout whole range.
I tried MDR Z1R and Beyer T1/2 (600ohm) phones.
Good luck getting yours sorted out.
PS - I don't use MQA so haven't checked it.
Thanks for the feedback jirams. Enjoy the awesome sound of the sig.
Just out of curiousity, which of those phones do you like better, and why?