I am an audiophile and electronic engineer. I dont know everything, but I happen to have two friends who are a dealer for high end and the other one is importer/distributor for high end, here in Brazil. I usually do product testing for them, purely subjective, no measurements. I love to do it, so I do it for free, and when I think I reached a reasonable conclusion, I invite them to come and listen by themselves. I keep doing it because of the joy of testing super high end equipment that I get to keep for several weeks at a time.
Enough introduction, here are MY findings, based on my experiences and the products I have tried:
1. If you have mid Fi it is difficult to hear some of the differences. Some products really shine when you have a set up with enough resolution.
2. The quality of your network is very important. It is not the same to listen to Roon in a regular network vs one with a good audiophile switch, external power supplies and clocks.
3. Roon can sound very very good, and be completely satisfying. Depending on the demand of the listner, you may need a very good audio server/network/DAC to achieve the maximum sound quality Roon can give.
4. Having said the above, under the same super high end set up, music will still sound a tad better when playing with a plain vanilla UPnP App. Of course, you cannot compare the user experience to using Roon.
So there you go, Roon can be very very good, but an App like BubbleUPnP, while not giving so many goodies like UI and DSP, can sound a couple notches better.