Thanks for replying, I've found the other slider but when I set jriver for system volume it makes no difference.
I'll try the alsamixer
Do you have any instructions
Regards
Open a terminal and type alsamixer. Press f6 to select your sound card/dac (arrow keys, enter). Then you should see something similar to the attached image. The options that says Headphone (or headphone impedance at the top where it's not cut off) is the gain. Use j or - to decrease k or + to increase that when it's selected. The option might be named differently for you, since this is a soundcard that's ment for headphone use specifically, it's called "Headphones Impedance". Look threw all the settings and see if you find something useful.
I have dacs/amps that don't have this setting. Or instead have a physical switch to change this. There is no guarantee you have it. But if you do it can change volume dramatically.
Though, since you said "same dac etc." probably you do not have this setting. Since when you have an external standalone dac connected to an amp I don't think there is any way this could be a setting controlled from software.