So many volume controls...which one to use?

[Shoomba]

Equipment (with short names for reference):
 
Sennheiser PC 360 Gaming Headset ("Headphones")
Little Dot I+ 6JI X2 Tube standard Hybrid Headphone Tube Amplifier ("Amp")
Astro Mixamp ("Mixamp")
Behringer UCA202 Audio Interface ("DAC")
 
Summary:
 
I'm new here, so thank you in advance. I recently bought a new computer, and decided to get a decent headphone amp to go along with it.  I can already tell a difference, my music sounds fresh and I'm finding myself enjoying just listening to music more than ever before.  That said, I'm struggling with one question as a result of my new gear: which volume control to use?
 
Connections:
 
PC ----> DAC (USB Connection)
 
DAC ----> Mixamp (Optical Connection) [note that the Mixamp is also connected to the PC by USB for voice communication purposes, but not really relevant here)
 
Mixamp ----> Amp (Analog connection - Y-Cable)
 
Amp ----> Headphones (Analog connection)
 
The PC, Mixamp, Amp and Headphones each have volume controls. 
 
 
Background:
 
To attempt to head off a few questions:
 
1. I've used the Mixamp because I commonly game at night, need both voice communication as well as game audio, and it's worked well for that purpose.
 
2. The DAC has been inserted (understanding that I'm not actually using it to convert Digital to Analog) because the new computer doesn't have an optical output (which is required for the mixing features of the Mixamp. 
 
3. I searched and reviewed the following threads:
http://www.head-fi.org/t/775149/dacs-with-digital-volume-control
http://www.head-fi.org/t/759708/help-with-setup-external-volume-controller-dac-amp
http://www.head-fi.org/t/769979/how-can-i-get-this-to-work-speaker-active-pre-amp-volume-control-and-macbook
http://www.head-fi.org/t/63399/volume-control
 
*EDIT:I also reviewed http://www.esstech.com/PDF/digital-vs-analog-volume-control.pdf (which was the basis for the PC at 100% and trying to get the Mixamp as high as possible).
 
My current solution:
 
I have the PC at 100%, Mixamp at about 80%, the Headphones at about 80% and I use the Amp as the primary volume control, but I've played a bit with volume on the Headphones and Mixamp.
 
I'm open to any suggestions (or any general knowledge/suggestions), and thank you. 
 
*EDIT: see above.

 

[MindsMirror]

You should usually keep the headphone's volume control at maximum. The volume control on the headphone is a variable resistor which increases in value to reduce the volume. Adding resistance to the headphone is equivalent to adding output impedance to the amp, which is undesirable. It wastes power from the amp, and can alter the frequency response of the headphone.
 
If you hear noise from the amp, in that case lowering the headphone volume might help to reduce it.

 

[Shoomba]

  You should usually keep the headphone's volume control at maximum. The volume control on the headphone is a variable resistor which increases in value to reduce the volume. Adding resistance to the headphone is equivalent to adding output impedance to the amp, which is undesirable. It wastes power from the amp, and can alter the frequency response of the headphone.
 
If you hear noise from the amp, in that case lowering the headphone volume might help to reduce it.

 
Very helpful.  Will make that change. 
 
Should I also try to run the Mixamp at 100%?

 

[MindsMirror]

 
Should I also try to run the Mixamp at 100%?

In general, yes. As the ESSTech link explained, it should be at 100% for the optimum SNR. Although, there's little harm in lowering the Mixamp's volume for the sake of convenience. If you can turn down the Mixamp and still don't hear the noise floor, that may allow you to set the Little Dot's volume control at a more useful range. An overly sensitive volume control can be a problem with powerful amps and/or sensitive headphones.

 

[Shoomba]

Thanks -- that was my suspicion based on that link, but I thought I heard noise being introduced by the Mixamp at higher volumes (though possible that it was in my head).
 
Very very helpful!

 

[nottheface]

In a more simple setting, is it better to use the amp volume control, the windows volume, or the software volume (e.g. iTunes or Spotify)?  Headphones are AKG 7xx, with a Modi2/Vali stack. 

 

[Shoomba]

Based on the responses above, I think you want to max the digital volumes (PC and program) and then control with your amp.
 
If you need to tone down the PC master volume to keep it reasonable, I think you could do that, but it would be best to keep the PC at 100%.