[cottonchipper]

My setup for headphone listening is PC > Hifiman HM-101 line out > O2 > Fostex T50RP.  Since adding the O2 I now have plenty of power for my headphones, but I'm wondering about the correct way to set the volume.  Should I set the PC volume all the way up and use the O2 to adjust to the level I want, or have the PC setting somewhere lower than maximum volume? 
 
Also, is it generally better to use the "Gain" button on the O2 to help reach the desired volume level?

 

[MemoryLeak]

I am interested in this as well. I have been setting my PC or Laptop all the way up and setting desired volume on the amp.

 

[OkawaiiO]

What I do is keep the pc volume at 100% because its digital it doesn't distort. Then use the volume control on the O2 to change the actual volume. 
 
For the gain I don't think u should use it unless u feel that without the gain the volume is not enough for u.
 
(just my opinion ><)

 

[recepky]

since I am using jriver media player, I leave the sound card volume 100% and in the jriver options I set the volume option to "internal volume" which is 64bit volume control, so I am using jriver volume mostly and I leave the sound card volume 100%

 

[Head Injury]

Set the digital volume as high as you can while keeping the O2's volume control above 9 o'clock or so. The O2's volume control is solid, but turning the volume too low will still adversely affect noise, crosstalk, channel balance due to interference in circuitry itself. The gain stage is placed at the input not the output, so you aren't lowering the volume of the circuitry.
 
I recommend using some kind of digital volume control, either lowing the system volume a little or using ReplayGain. Some DACs will clip, distort, or otherwise perform worse with a 0 dBFS signal, even just -1 dB of attenuation can help avoid this. Besides, digital volume control isn't the evil some people think it is. Read my messy post here for a basic explanation.

 

[Pirakaphile]

I'm running VOX audio through my computer and have it at 100%. My Schiit Magni has all the control of power, which is sometimes a little difficult for low impedance cans, since just the tiniest turn can result in double the volume, but I like to know the volume control is a physical change, rather than one in the programming of the computer.

 

[ailseman8]

Set the digital volume as high as you can while keeping the O2's volume control above 9 o'clock or so. The O2's volume control is solid, but turning the volume too low will still adversely affect noise, crosstalk, channel balance due to interference in circuitry itself. The gain stage is placed at the input not the output, so you aren't lowering the volume of the circuitry.

I recommend using some kind of digital volume control, either lowing the system volume a little or using ReplayGain. Some DACs will clip, distort, or otherwise perform worse with a 0 dBFS signal, even just -1 dB of attenuation can help avoid this. Besides, digital volume control isn't the evil some people think it is. Read my messy post here for a basic explanation.

Would the same 25% volume rule apply to something like a fiio e07k where the dac and amp are integrated? I have been wondering what to do here as well.