You could easily do it if you got a midi controller. Just tested it. I have Kore 2.1, but any thingie with knobs and sliders would work. You have to add your midi controller in the midi setup (click, that's it). After you checked this, just right click volume in your pianoteq, and then midi - a message pops up, you move the knob or slider of your choice, and it is assigned! Easy. So you could then turn that knob instead of using your mouse.
You can "automate" many things in pianoteq like this.
Same method works of course too for your sequencer, I use Reaper, and you can assign the volume slider of your pianoteq track. Depends on the host how to set it up.
Don't think there is a keyboard shortcut - you mean say key 1 would reduce volume and key 2 make it louder? There are so many things that are possible, but I have no clue if that exists.
If you're aim is to adjust the volume of a track you recorded with pianoteq - you could use the automation feature in your host (again, here Reaper, but any host has that, volume automation) to make some passages louder and others more quiet than you played them in first hand.
