In this case, the volume error was out of the mastering engineer's control. After the 5.1 & Atmos mixes were mastered and given final approval, the masters (probably .WAV for the 5.1 and ADM for the Atmos) were converted to Dolby TrueHD by the Blu-Ray authoring team. Dolby TrueHD has a built in "
dialogue normalization" setting that sort of acts like an automated volume control.
As I understand it, our processors at home (AVR, Blu-Ray player, etc) automatically lower the gain based on the difference between -31 and whatever the assigned dialnorm value is. Both albums should have been assigned a dialnorm value of -31, meaning that the overall level would be unaltered because 31 - 31 = 0. However,
Waka/Jawaka was assigned a value of -26 causing the overall level of the mix to drop by 5 dB.
The Grand Wazoo was assigned a value of -18, so the level drops by a whopping 13 dB. If you rip the 5.1 mixes to a digital file format like FLAC, the dialnorm can be bypassed. Unfortunately, there's no getting around this for the Atmos mixes because they have to stay in the encoded TrueHD format for all channels to be extracted.