how to assign pianoteq volume to midi controller?

If you click on the Options tab on the main User Interface, and then click on MIDI, you will be presented with a list of Midi Continuous Controller numbers, and their corresponding effects upon Pianoteq.  In the case of Volume, you will notice that Pianoteq (as well as a wide majority of other musical plugins and hardware) is hardwired to correlate audio volume with CC#7.

So, if you are able to assign a fader on your keyboard to send Midi Continuous Controller #7 to Pianoteq, then you are in business!

HINT:  If you do decide to permanently assign a specific keyboard controller to send CC#7, you may have to "waken" Pianoteq's response to this controller.  In such a case, you may seem to hear zero volume upon first opening Pianoteq; your countermeasure is to push the keyboard's controller to full-on, then pull back to full-off, and finally to some midrange value -- to align the output of your keyboard to Pianoteq's receiving input of CC#7.

Hope this helps,

Cheers,

Joe