Thank you for doing this, very insightful with the blind taste test!
For the P with flats it was very close for me between the Noble and Luce, I think they sound remarkably similar in the first round through my Audio Technica headphones. Both have a well-rounded sound that appeals.
In round 3, the Mantle stood out to me for little more with that sparkle in the highs.
So overall, not a clear cut one for me at all, they all sound nice and ultimately I feel like I'm splitting hairs. However, I am very impressed by the Luce. I will probably pull the trigger on one of these at some point because I can imagine it being an absolute gem when paired with other preamps that are taking a tone-shaping role. Intrigued to hear what it would be like adding some warmth to the harshness of my Rusty Box, or some valve goodness after a DCX Bass.