A pic is worth a thousand words...but here are some more words anyway, lol.
called subs no BM and no boost refers to a sweep in channel 4 with no bass management and the +10db for pcm unchecked.
As soon as you turn on BM the sweep is 10db lower and you need to check the box for +10db for pcm. The advanced audio codecs
get decoded to pcm before bass management, eq etc. I had just previously assumed that the default +10db for dolby and dts would work for dolby truehd and atmos and dts-master and dts-x but clearly not.
Note that if you check the +10db box for pcm and don't use BM it will add an additional 10db of boost to the lfe channel (channel 4). It was awesome for the brief time I did this but not really what I want for balanced sound.
I've copied and pasted an explanation Sanjay from Datasat/ATI emailed me, I don't think he'll mind me sharing:
the LFE channel is supposed to be played back 10dB louder than all the other channels. This 10dB boost cannot be done in the digital domain because it would cause clipping. So the 10dB boost is applied to the subwoofer output when the signal is in the analogue domain, after D/A conversion. Discrete bass from the LFE channel is usually combined with derived bass from other channels to create a subwoofer output. Problem is, if the 10dB boost is applied to the subwoofer output, it will cause the discrete LFE bass to play back at its intended level BUT the derived bass from other channels would be 10dB too loud. How to avoid derived (non-LFE) bass from playing back 10dB too loud?
Before combining discrete LFE with derived bass, the level of the derived bass is dropped by 10dB. That step has been part of bass management since the LFE channel was introduced to consumer audio. Now when the 10dB boost is applied, the discrete LFE plays back at its intended level (10dB louder than other channels) and the derived bass plays back at its intended level (same level as the other channels). Dropping the level 10dB only happens during bass management, because bass from other channels is included in the subwoofer output. If bass management is not being used, then no need to do the 10dB drop (only discrete LFE is going to the sub). "