Leveling has to do with how aggressively Dolby Volume tries to level volumes. There are 10 steps above OFF. Dolby mandates a factory default of 9 which in my opinion is too aggressive, so you might want to dial it back.
Half Mode has to do with whether frequency based volume adjustments are applied. With Half Mode off they are always applied. With Half Mode on they are only applied if the combo of content volume and Main volume knob setting is such that the output is lower than some threshold Dolby has picked. I.e., with Half Mode ON they don't do frequency based adjustments if the output is already loud enough you should be able to hear everything. Apparently it is strongly recommended that Half Mode be left ON (the default), but Anthem exposed the ability to turn it off if you want to experiment.
That leaves the Dolby Volume setting itself and the mysterious Calibration setting (which is found in the Level Calibration menu). The Dolby Volume setting gives you choices of OFF, Music, and Cinema Reference. If Dolby Volume is OFF, no Dolby Volume processing happens for that Source and the other Dolby Volume settings are irrelevant. Set Dolby Volume to OFF if you don't want to futz with Dolby Volume. Apparently Dolby mandates a factory default of ON, so if this is the first firmware install you've done that included the Dolby Volume feature, you will find it set to Music (or Cinema Reference -- I forget which) for every Source. So just turn it OFF for every Source until you are ready to play with it. Subsequent firmware installs will preserve your setting here for each Source.
Dolby Volume Music is "normal" Dolby Volume processing. This is the one you will use for most content. Volume leveling will occur according to how you have set the Levelling control (no leveling if you turn that all the way down). Frequency based volume adjustments will happen either all the time or only when the output volume is soft (the default) depending on how Half Mode is set.
Dolby Cinema Reference is apparently identical to Music except that it boosts output volume by 10dB (or perhaps 11dB). Apparently the idea is to take a 75dB home theater setup and make it work like an 85dB Movie Theater setup. Personally, I don't see the point.
Note that while viewing any Source you can view and adjust the current Dolby Volume setting (Off, Music, or Cinema Reference) by pressing the "0" button once and then using the Up/Down arrow buttons. Any changes you make this way will be recorded (i.e. permanent) in Setup > Source Setup for that Source.
All of the above is remembered "per Source".
Meanwhile over in Setup > Level Calibration is the mysterious Calibration setting for Dolby Volume. So far I have not found any good reason to change it from the default 0dB setting *EVEN THOUGH* that does not give me a 75dB SPL test tone from that line in Level Calibration. I do *NOT* know what this Calibration setting is supposed to do, nor why you might want to change it.
The fact that a Calibration setting of 0dB appears correct in my setup (despite the SPL reading) may also be due to the fact that I have ARC active. I just don't know.
Simply put, the choice (per source) of DV Off/Music/CinemaReference and the choice (per source) of Leveling value for whenever DV is set to Music or to Cinema Reference, are likely the only two settings you'll want to fiddle with.
ETA: NOTE 1: The Dolby Volume Calibration setting in Setup > Level Calibration will show as NA if the current Source has DV turned OFF. But if you go into Manual test mode to play the test tones, the current setting will be visible and changeable again even though the current Source isn't using it.
NOTE 2: With Dolby Volume active for the current Source, an additional display happens in the cycle of displays when you press the Select button repeatedly. The new display shows how much Dolby Volume is boosting or attenuating the volume level at the moment.
NOTE 3: With Dolby Volume active, expect you will have to LOWER Main volume more than you are used to. This will be particularly true if you are using Cinema Reference of course. The trick appears to be to lower Main volume until the loudest passages are no louder than you want for your current listening circumstances. Volume leveling will then RAISE the volume of softer passages (and frequencies that are harder to hear) so that you don't miss anything.
--Bob