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. 
You will need to know the input sensitivity of your pre amplifier. If it is too sensitive for modern digital sources (which is often the case), you get clipping of the amplifier input circuitry, and that sounds really nasty. A telltale sign would be if you do not have to open the volume control on your amplifier very far to get a loud sound. See here: If this is the case, it is wise to reduce the output level of your DAC somewhat using the volume control on your laptop. Modern DACs have enough internal bit depth for this. If the mismatch is too great, it may be better to use inline attenuators.
Why even have a lap top there are so many better solutiins ,and much less noise
Heat pipes instead of fans, Solid state drives vs spinning disks.
The prices have come way down ,as well as players.  Just  a solid alternative solution.
Many integrateds allow you to separate the pre-amp from the power amp either by way of a switch or jumpers.  You'll get the best sound by far by bypassing the preamp and going directly to the power amp.  The amount of clarity and openness lost by going through even the highest quality preamp is amazing.
Willem, thanks for the Harbeth article. As it turns out, because previous sources used hadn’t the option of adjusting output amplitude, I simply failed to consider its potential impact on overall reproduction. It helps to understand why, between two different laptops, there was such a significant difference in  sound quality between the two.  I don’t know if it’s the only reason or even a reason at all, but the laptop with the least desirable sound, Sony, had an output setting nearly at its highest level; the other, an Apple, (the one now connected) had its setting close to null. 

I will continue to use a laptop in this setup primarily because it sounds wonderful as well as the fact that it provides a means to easily and conveniently sample various artists and genres for ultimate potential use in my main system. 

My primary setup consists of several sources including shanling CD 100, Angstrom 200 preamp, Ayre V3 amp and Martin Logan Ethos speakers. Though quite different in several ways I enjoy both systems very much.