I see you posted on teajays ZOTL thread, that makes sense, the thing is you are comparing preamps that are targeted for either the neutral, realistic, studio crow or the warmth euphonics mushrooms crowd.
The thing with the Supra is I prefer it so far on the 6SN7 stage, I wanted to experience the DHT stage but I was surprised how good the 6SN7 with its stock tubes is.
I am a tube roller but 2 preamps shown me that the tube it does not matter if the designer built the preamp around a specific tube set.
Take Ralph, his preamps with the stock Chinese Shuguang orange base 6SN7 is almost perfect, I tried the others and yeah you get different flavors but the stock tubes are very good and for comparisons I always go to these.
Mick with his EH tubes wow, you need to hear it to believe it.
Neither Ralph or Mick speak much about tubes and tube rolling, they say that yes sound could be improved but their preamps are excellently designed even around the stock tubes.
I wish I could remember the tubes on the ZOTL, very very neutral, not detailed but that could have been the source most likely and very musical and..... Let me find a good adjective, circumspect? Polite?