@amirm :
I'm absolutely not sure you measured the main AKM DAC at ZONE2 output.
There are 2pcs PCM5102 TI stereo DACs on the board (right up next to AKM) for ZONE2 and Subwoofer outputs. These are responsible for driving the above 2 outputs, even when the main zone and zone2 plays the same music or different. It is necessary use separate DACs there to be able to provide you can also play back separate sources in the MAIN ZONE and ZONE2 same time. According to see a bit closer the main AKM DAC, there are numbers (2-4) of NE5532 opas around there, because of dual-differential DAC configuration needs many opamaps for I/V and filtering, so the number of NE5532s are OK, no other ones for ZONE2. IMHO, because of the ability to drive simultaneosuly the MAIN and ZONE2 there are no separate digital and analog signal path routing/switching (I mean using the main DAC for all zones output - and separately analog routing of signals, different DACs). So Denon decided to use digital only, the Zone2 and for Subwoofer wit separated and much simplier DACs. This may explain your bad results.
I'm absolutely not sure you measured the main AKM DAC at ZONE2 output.
There are 2pcs PCM5102 TI stereo DACs on the board (right up next to AKM) for ZONE2 and Subwoofer outputs. These are responsible for driving the above 2 outputs, even when the main zone and zone2 plays the same music or different. It is necessary use separate DACs there to be able to provide you can also play back separate sources in the MAIN ZONE and ZONE2 same time. According to see a bit closer the main AKM DAC, there are numbers (2-4) of NE5532 opas around there, because of dual-differential DAC configuration needs many opamaps for I/V and filtering, so the number of NE5532s are OK, no other ones for ZONE2. IMHO, because of the ability to drive simultaneosuly the MAIN and ZONE2 there are no separate digital and analog signal path routing/switching (I mean using the main DAC for all zones output - and separately analog routing of signals, different DACs). So Denon decided to use digital only, the Zone2 and for Subwoofer wit separated and much simplier DACs. This may explain your bad results.