Optical = Marantz DAC
RCA = Marantz Pure Direct Maybe.
Perhaps
@peng can chime in here because my experience is with the older Marantz AV8801. My guess is that if bass management is engaged then and producing sound from the subwoofer for 2.0, then there is an analog to digital conversion. When AD occurs, you are using the Marantz DAC.
- Rich
Optical = Marantz DAC, i.e. the AK4458 should be a know fact, there is no other way.
Your point about bass management (not the double bass thing alone..) is a what caused me to starting doubting my previous assumption that direct/pure direct would bypass the ADC/DSP/DAC blocks.
So now I agree that RCA analog input is a different story that require further digging.
a) If direct or pure direct modes are engaged, and the left/right speakers are selected "large" the signal might bypass the ADC/DSP/DAC path, and go directly to the volume control block instead. It was shown on multiple pages in the service manual that the direct path and the ADC path both exist and are selectable via the NJU72750 switch. Obviously the "double bass"/LFE+Main feature would still be allowed, it could be implemented independently so it does not have to be a negating indicator imo.
https://datasheetspdf.com/pdf/1100592/NewJapanRadio/NJU72750A/1
I have to say "might" because they may or may not have implemented the selectable "bypass" feature.
b) If direct or pure direct modes are engaged, but left/right speakers are set to "small" then all the bass management features appear to be intact, including the crossover settings, so that indicates the signal have to go through the ADC/DSP/DAC path.
I may email Denon/Marantz for clarifications, in the hope that one may just respond, but I won't bet money on that either..
Denon support (If true, it is reasonable to assume the same would apply to Marantz) did have the following to say about pure direct mode but still not 100% clear because: How can dsp processing be "not used" if some bass management features remain? That's why I guessed that there are caveats to go along with the so called direct/pure direct modes, such as setting speakers to "large".., but that's purely my own educated guess..
"......If you're a purist, yet still want the benefit of using all the speakers of your home theater system, we suggest that you consider Denon's Pure Direct mode for bypassing all DSP processing. Pure Direct will provide a 2 channel or 2.1 channel output that doesn't use any DSP processing from the receiver."
https://denon.custhelp.com/app/answers/detail/a_id/68/~/choosing-surround-modes