Hi
Scrolling a bar through a track is OK, but scrolling through a bar for volume is very strange in my opinion. It is nearly impossible to fine tune volume with a finger on bar.
Why not a +/- system (as on Audirvana itself?)
I have iPad mini and iPhone.
Kind regards
Thierry
Try the volume buttons on your phone or tablet.
That’s always worked for me. 
Hi
I use Audirvana on UPNP, not on USB, on an Esoteric N05XD.
Ipad volume buttons do not work to tune volume.
Currently, I use the Esoteric remote for volume as Audirvana volume control is really not usable for me.
Regards
Thierry