Where do I set volume control on NAD M51 DAC?

I have a C510 which is supposed to be the same circuitry inside. Direct to amplifier it could be harsh & analytical at higher volumes; dull & muted at lower volumes.  Adding a (tube) preamp helped immensely; however as it doesn't have a remote, I find myself using the Nad's rather frequently.  I can go from about -3db to about -20db before noticing any difference and getting up to change the pre's volume manually. I'm sure much of this is system dependent.

I don't think those figures are correct as the NAD has a different stepping than one might assume. I know the actual top output is 2.375V SE and double that for balanced. -10db is just ten steps from 0db and the DAC can go to -55db before actually truncating a 24-bit file. While I can't say the exact voltage, I am sure the voltage is far closer to 2V at -10db than 200mv. This volume control is from a digital sense 210db in range.

Between the technical measurements and number of user indicated preference, the range that most prefer is between -6db to -10db. If you have a good preamp setup, it won't present any issues. 

Well, 
At 0db your DAC output level is 2V; at -10dB the output level is 200mV respectively. 
By supplying 200mV instead of 2V you simply void overloading that causes distortion and significant loss of tonal balance and dynamic headroom.

I have a Primaluna integrated with the following input specs: 

Input Sensitivity: 320mV 
Input Impedance 100k Ohm

Does that help at all?  Thanks Czarivey!

It depends on sensitivity of your preamp.
The idea is to fill up the cup so you can bring it to the table without spilling :)

Wow!  The knowledge base on this forum is amazing. Thank you!

-10dB sounds about right to my ear.  Settings closer to 0 dB seem a tad forceful--like volume wars stuff. 

While true that digital volume controls can truncate the dynamics in music when applied to significant degrees, the NAD M51 has a 35-bit over the more typical 32-bit digital volume control implementations, giving it a bit more room before it begins to truncate the digital signal amplitude.

During the measurements via Stereophile, the small amount of overdrive that won't be any issue for nearly any premap, had increased the noise floor of the DAC notably. When lowered to -10Db, it was able to achieve 21-bits of genuine resolution across the audio band. I still believe that M51 is a benchmark for digital volume control implementations, I would agree that too much digital attenuation will prove detrimental to the audio signal.

The Nad only puts out 2.375V SE at full output, a little over the Redbook standard and should pose no overload problems for any well designed preamp.
If you do reduce it, try to stay at 75% or higher, as some digital domain volume control can "bit strip" if below 75% of full output. EG: 14bit resolution or 12bit and further if it’s very low.
Thorsten Loschech of AMR, says he can hear a detriment of just a small -10% reduction from full up, on digital domain volume controls. I can’t, it needs to be -25% or more for me to hear it.

Cheers George

Thanks mmeysarosh!  I'll try -10dB

While there doesn't seem to be a clear exact figure, there seems to be a general consensus that -0 db is a bit to high. Noted by many through listening as well is measurements taken by Stereophile, where the DAC performed better at -10 db then it did at -0 db on their Benchmarks.

http://www.stereophile.com/content/nad-m51-direct-digital-da-converter-measurements#yAwtilFGs7kixtPK...

Also note that at -0 db, the voltage is slight bit above standard and a little of the volume seems to be the best route.