Yes and yes.
The Kurzweil pc3 has only 9 sliders so I sometimes switch between 2 assignments. Usually I have it on “get defaults from plug-in” and then the sliders control the 8 Quick Control for the virtual instrument on that track. Otherwise I use a preset that handles volume/panning/hi-cut/low-cut and it automates the audio mixing functions while still in the project window.
[As an aside, it would be nice if Cubase would let me enable one assignment for all tracks - that is,have all the QCs on all tracks function as send levels without having to switch manually. That way you could just use the arrow keys to move through all tracks quickly. I wonder if anyone else has a way of dealing with that]
The same can be done with a midi track and rack instrument. The plug-in quick controls will be on the midi track and the audio QC’s will be the the audio track.
Are you having difficulty assigning your knobs/sliders, or getting them to control the instrument track?