Check out Robert Deutsch’s review of the Montis in Stereophile. He tried 3 different tube amps, including the PrimaLuna Prologue Premium integrated, and a Simaudio W-7 ss amp. He ended up liking the McIntosh Mc-275 the best.
I own a pair of the Summit Xs. They’re a great speaker aren’t they? I was using a Pass XA-30.8 but knew that "technically" the speakers could use more power. So I tried a D’Agostino Classic Stereo amp which has more power and doubles down to 2 ohms. The result is a more relaxed, cleaner sound that keeps me in the listening chair listening longer. The D’Agostino is more expensive and that could explain the difference, but I think the added watts and doubling down are significant.
I would like to try out a good strong tube amp with the Xs though.