amplifier with volume control

The presumption that an amp with volume control built in will automatically yield superior sound quality is wrong. It may. It may not. Only comparison to other genres/systems would tell. 

NO one can tell you which configuration would be superior in any combination of gear; pre/no pre, passive/active pre; dedicated DAC direct/integrated DAC direct; dedicated DAC with integrated amp, etc. 

I have tried all these and the winner? It depends on the setup and gear. 
Anyone who tells you differently is simply stating opinion. You simply have to try combinations if your goal is to actually find the best method with the gear on hand. Short of that, just presume and pick; it's what most do. 

I have built a lot of systems using DAC direct, either dedicated DAC to amp with software attenuation, dedicated DAC to integrated amp, or integrated DAC with hardware (built in) attenuation. Again, results vary based on the equipment, cables, etc. used. One can have a favored setup, switch speakers and find that a different setup is preferred. 

It is nowhere near as simple as recommending one setup as superior. The more systems built, the less a simplistic setup recommendation suffices. Unless you build a bunch of rigs, you simply will not know which is best method with your gear, and neither will anyone else. 

FM Acoustics amps have gain control for each channel in the back panel and Vitus Audio used to have the capability for variable output or fixed for 2 sources (not familiar with current models). For example, the VA  SS 101 sounds great alone and there is no need for preamp.

I prefer the name of potentiometer for the volume switch.  It just makes it sound like it is holding all the answers.  This may sound strange but I have my "cheap system".  This runs a class D amp to some transmission line speakers that I built.  I only run through this through bluetooth.  So, should be a crap sound, not going to argue things could be much better.  To maximize this, I run the volume switch on the "integrated D amp" at 2/3 potential.  I then adjust the volume from digital source.  This makes the speakers much more alive and dynamic at all volumes.

I’ve used passive preamps in the past but they’re quite limited in application due to loading effects. A power amp with volume control would also limit one’s choices. For my application, an integrated amp was a better choice.

It depends on the amp and the optimal level of gain required.  With an amp that is extremely sensitive, (for example Art Audio PX25 or Diavolo is driven to max volume at .5v input) a passive preamp is preferred.  With amps that are less sensitive, higher gain in the preamp and a higher output is preferred and will deliver a better sounding experience.  

The key is choosing the right option for the power amp in question.  There is no "best option."  There are best options for that particular amp and system.