[G1zm0]

What I mean is low gain & volume knob in higher position vs high gain & volume knob in lower position.
So, I've seen many discussions already, but there's no uniform consensus between users.
So, I checked with producer and they have pretty definitive answer for this question.
Can I consider this topic closed? At least for JDS Labs amplifiers?

Here's screenshot from their manual for atom amp+ (it's same for original atom)

 

[Raketen]

Not an expert or anything, but I believe a common misunderstanding is the idea that raising the gain setting also increases an amp's capabilities (i.e. "headroom"), but the general case is rather that gain is affecting loudness relative to those capabilites (sort of like if you just changed the input's level). Higher gain also tends to be associated with increased noise and distortion levels.

Correspondingly, a high volume position at low gain does not generally mean that you are somehow limiting the amp's performance.

Maybe there exist some designs that behave differently (like with multiple operational modes or something), or use terms differently, or I could also just be completely misunderstanding. Personally I just do the same- try to maximize the useful range of the volume knob for a given headphone.