Best way to route signal from laptop to integrated amplifier

I’m writing this regarding my secondary system which I spend more time with than my main setup. It’s in my garage away from the household business in our listening room which also serves as our living room. I listen in nearfield mode no more than 6 feet away from the setup which consists of an Apple laptop, Dragonfly USB DAC,  N.E.W.  P3 Tube preamp,  old Russian integrated tube amp of unknown manufacture or class, and B&W  CDM1 speakers. 

Thats the configuration I’m using now and, of course, I’ve experimented with other routing including (1) analog out from the computer direct to the integrated amp;  (2) same but with the Dragonfly between the computer and amp and  (3) computer to Dragonfly to preamp to amp.  This last configuration seems to be best and sounds incredible especially for solo guitar which I mostly listen to. 

Anyway, although I have come to prefer this mode of listening and believe this system as it exists now needs little change but a conversation that I recently had with someone who seems to have the experience and knowledge necessary to take to heart had a suggestion. Because my amplifier is integrated he recommended that it’s volume adjustment be set at maximum and use the preamp to adjust for desired listening levels. I’ve tried various settings on both but my ability to detect subtle differences may not be good enough for accurate evaluation of which way is best. The question, then, is whether there is a generally accepted method in the Audio world to these settings both in regard to sound as well as equipment.