I have a supra usb cable in my setup as well, plus two others.
I think tweaks like these that you are trying are really worth it. For instance, i like the overall tonal balance better through my headphone setup. This tells me i can get the perfect cable combination with my speaker. I am not far from the perfect sound. Swapping some power cables is well worth trying also. The impact on bass is significant. In my case, a little more in the upper mids, and i will be done. This is the magic ingredient that can make the sound really really involving.
But believe it or not, the r2r 7 still is improving, though very slowly, after 1300-1500 hours. Kind of crazy, really. At this point, i am very happy with it most of the time. With the hifiman he-560 through the nfb-1amp, using a balance headphone cable, i am really really happy with how it sounds. I know i can still tweak my monoblock amps to improve them a little. I just got them new enclosures, but the layout still need some work. All details matter really and the r2r 7 is a good base to work from. The source is a key ingredient to good sound.
By the way, i ordered a r2r 11 for the office. Got a chance to listen to it before ordering, it sounds way beyond what it costs, with great soundstaging and clarity. I think it's a steal.