No and no, it has nothing to do with gain, all these days have set gain for their amp sections, line out sections, you are not adjusting the gain in analog domain, bit in digital. There is no amping. Signal is being attenuated before it gets converted. Simple as that. Rest of the circuit is fixed, as in it always works at the same gain in it's analog domain. Has absolutely nothing to do with double amping. Double amped is when you would plug your headphone output into a nother bigger amps input.
If the volume is adjusted digitally it can be adjusted for any output, doesn't matter if it's line out or hp out balanced or se. The line out will still be unamplified line out, with a lowered volume level. What's hard to understand here. Most manufacturers don't include adjustable output for line out cause of time, costs or just being plain lazy.
A line out section of a dap can be take straight from lpf or go through a buffer stage(buffer being the better option) and it doesn't give any gain, rather you are turning the volume down from 100 to something else, whatever the reason may be.
Lastly volume has nothing to do with amp section in these devices, it's either xmos chip, FPGA or DAC chip itself.
Also volume control is not a gain dial, rather a brake dial. You are not adding anything, but rather removing to make the signal quieter. And it's a passive component that takes care of it.
