Thank you very much for your professional response and recommendation.

So I set the ADI-2 DAC Reference level to -5 dBu and Volume to 0 dB. I noticed that I need to increase the listening volume by about 10-15 dB compared to the previous setting (Ref Level + 13 dBu and Volume -4.5 dB) on the preamp. The average listening volume was about 55-60 dB (scale on the preamp) and with the new setting it is about 70 -75dB (depending on the type of recording).

The original (inappropriate) setting of Ref Level + 13 dBu and Volume -4.5 dB was done according to the ADI-2 DAC manual see page 66 (paragraph Fixed Output Level - Lock Volume) see https://www.rme-audio.de/downloads/adi2dacr_e.pdf  where it states:
"For example when the analog output should operate like a typical HiFi unit @ 2 V output level (RCA, equals +8 dBu), set the hardware Ref Level to +7 dBu and Volume to +1 dB. Or +13 dBu and Volume to -4.5 dB."
But these are values for RCA and not XLR.  So apparently I somehow incorrectly deduced that Ref Level +13 dBu and Volume -4.5 dB is for XLR. So I hope that this incorrect setting (that I used XLR values for RCA) could not have caused some damage to the device - both ADI-2 DAC and M8sPRE preamplifier.

I was of course intrigued by the other details you mention.  So please allow me a few questions:
As you write, the specification in the M8sPRE manual on page 12 states for XLR:
Input sensitivity 0.352 V
Overload margin 12 dB

I would like to know how you calculated that the highest input that XLR can accept will be 1.4 V or +5 dBu?  Could you please explain this a bit?
What would lead a manufacturer to quote these values? Or could it rather be a mistake in the manual? If I look in the manual for the lower range M6S PRE AMPLIFIER on page 13 https://www.musicalfidelity.com/uploads … manual.pdf  it states for XLR:
Input sensitivity 4.4 V
Overload margin 12 dB
Are these values okay, please?

And then your recommendation to check with a 400 Hz sine wave.  I'd like to do that, but I'm not sure I fully understand everything.  So let me summarize the process as I understand it:
1. the RME ADI-2 DAC is in Fixed Output Level - Lock Volume mode.
2. I run this generator in my streamer (audio PC) https://www.szynalski.com/tone-generator/  and set a 400 Hz sine wave and set the volume in the generator at the link above to 100%
3.On the M8sPRE preamp I set the volume to minimum.
4.I will start the sine wave playback by turning on play at the link above and listen to the 400Hz sine wave signal from the speakers
5.In the next step I will stop the playback and make a new setting on the Na ADI-2 DAC. That is, I'll set higher values, for example Ref Level to +1 dBu and Volume to -1 dB, gradually increasing (for example Ref Level to +7 dBu and Volume to -2 dB and then higher), and then I'll gradually monitor the speakers for audible distortion of the 400Hz sine wave signal. Now here's the important thing - what does such distortion sound like? What kind of sound could I expect? Is there a sample somewhere on the internet, for example, please?
6.As a result, I will find out where the limit of distortion is and then set the level lower than the one at which the signal distortion occurred accordingly.

Thanks so much for the answers and help.

Thank you for your reply and other tips.

I just did 4 x testing with 400 Hz sine wave playback with this result:

The signal does not change in any way during playback from -5dBu to +13dBu and I did not notice anything. The only thing that changes is that the volume increases, but the signal itself still sounds constant.  Then I have noticed a clicking when switching levels (-5 dBu, +1 dBu...) but this is normal.

So can you please help me interpret the findings?  What would be the best setting for Reference Level and Volume? I can think of some middle values to use - could you please recommend?

Thank you

Thank you for your reply.

So I set the RME ADI-2DAC FS Reference Level +1 dBu and Volume 0 dB.

I also tried to compare the volume level with this DAC from MF M6x DAC https://www.musicalfidelity.com/product … es/m6x-dac

The referenced MF M6x DAC at the same source and when connected XLR, it turns out that the MF M6x DAC sounds louder than the RME ADI-2DAC FS.

My goal is to unify the loudness of the MF M6x DAC and the RME ADI-2DAC FS.

Would it please be possible to somehow find out from the parameters in the technical specification on page 12 see https://www.musicalfidelity.com/uploads … ssue-1.pdf what Reference Level and Volume values are set by the manufacturer for the MF M6x DAC?

And then I would set the Reference Level and Volume values on the RME ADI-2DAC FS in the same or similar way.

Thank you

@Jipe,

IIRC, according to your initial post, you mention only one source (PC) :
Is the MF preamp really mandatory ?
(Here, no more preamp : PC-> RME -> Power amp(s))

Season's greetings,

@KaiS

Thanks a lot for the reply. I've been adjusting the volume just by ear so that it's about the same, but can't quite achieve that. So it's possible that the RME or MF preamp could be playing louder - I'm not ruling that out.

I was intrigued by your device for setting the same volume - could you please elaborate on this specifically? Can a less experienced user of electronics like me use this? Or is it strictly for specialists?

I have been testing this for a long time and certainly didn't want to waste money on an MF preamp. But based on my tests I decided to go with the MF preamp.

My very personal quote: ADI direct to power amp(s) has too much dynamics !!!
How is it possible ?
Differently written, inserting an analog preamp (with buffers and so on) diminishes the dynamic span, and makes it more pleasurable to some ears.
For example, low level details are "better" perceived when the dynamic is reduced.

Enjoy the music, anyway.

Regards,

OK.
But, apart for a level difference, why would the insertion of a preamp give "better sound".
H2 ?