But "depending on source material " makes IMHO no sense ..
When I listen to modern "loudness brick" mixed content and then switch to older recorded music or 2.0 channel mixed down blu-ray movies I might want to go from +1 to +7 because of the volume difference in the content and how it hits the active speaker amps, I should maybe made it more clear that I'm still experimenting and unsure of the best setup and I'm now running two separate profiles on the DAC "depending on source material".
I think the objective is more
a) not to overload the analog input on the other side of the cable
(and to keep a little headroom just for the case, that you still want to use B/T)
b) to optimize / maximize SNR on both sides.
That's what I'm trying to do, my active speakers are expecting +4 db over XLR reference input, I have +1 or +7 to choose from and try to approximate by compensating volume manually. I'm not too concerned with the SNR noise coming out of the ADI-2 DAC at +7 db with a -35/-20 db roll off, it might not be absolute optimal but it is also inaudible, what is audible is the differences in the way the speakers active amps pick up and represents frequencies at +0, +1, +7, +13, auto ref, even when volume matched. Here the dynamics, soundstage, separation, detail etc sound the most right at +7 or +1, with modern "loudness" mixes coming in a little hot at +7 (this is when it goes from -20 db to -30/-35 db or) and older or less "bricked" recordings sound a little bit too flat, distant and lacking in detail dynamics etc.
This is why I wish there was a +4 db reference level stage, maybe then I could coax the most out of the both the DAC amp's SNR and also get the dynamics more even with contents of varying volume hitting the active speaker amps. Regardless, it works rather great as it is though, the unit is punching above it's weight more than more than I honestly expected.
This is pure imagination. Please read again manual page 497 and get a degree in engineering, hmpf!
Relax, I was not trying to imply that the auto ref feature is implemented in such a poor way that it is useless and negatively colors/deteriorates the units sound for all who use it. I'm just saying it did not work very well in my case, I suspect this is because the auto reference level stage never hits +4 db because it's a stage that doesn't exist in this DAC and the BM6A's being brutally honest and unforgiving active studio monitors calibrated for and expecting only +4 dBm over XLR it will not sound right and I'm much better off setting it as close as possible manually and compensating further by ear.
I somewhat have the same issue with auto ref in the headphone section with my HD650's, there it seems to be a impedance matching issue that the auto ref can't account for and they sound better in "hi-power" mode albeit with typical tell tale signs that they are running a smidge hot (in a fun and complementary way in this case) but there is no selectable ohm/impedance stages to manually set other than hi/lo-power and auto ref.
Not ideal, but it is what it is and It's not really detracting anything from my enjoyment of this little wonderful box.
RME AIO -> RME ADI-2 DAC FS "V2"
Sennheiser HD 650
Dynaudio BM6A "MKI"
Mogami Gold Studio XLR cables