@jeff_ss
Being an owner of Don's Vahalla tube integrated, might your "handle" more appropriately be "@jeff_tubes"? ;-)
I have the Triode Masters and heard the Sapphires and was not compelled to upgrade. However, the X-series is a different kettle of fish so I am enthused to hear them with Don and Lynn's newest electronics, presented in their best possible light. Oh, and the excellent Lampizator DAC which will clearly complement the rest of the gear.
I reiterate and amplify my love for these new mono's, which sounds cliche, but they sound like no amps at all, just masterful reproduction of the music in such an effortless and ethereal way... the sound is suspended in the air in the room with a completely realistic manner. The amps just completely get out of the way with a sonic signature that I would not describe with adjectives like "warm" or "cool", just completely realistic to the source of the music. This uncanny sound reproduction you will hear when you visit the room, of that I am confident. I hope I run into you and others on this thread in the room to get acquainted and share our impressions of what we hear.
I wish Charles would be there so I could meet him and applaud him on his excellent contributions on this forum, a paragon of audio knowledge and the utmost of civility. He clearly knows the sonic splendor of 300b gear. For me, hearing these mono's, it is a bell that can not be unrung. I think other attendees to the room might come to the same conclusion.