I heard the top Gryphon mono blocks in Ipoh Malaysia driving the Wilson XLFs - very fast and dynamic but the listening was too short for me to say I liked its tonal quality. Here in Hong Kong at the showroom of Gryphon's dealer I heard the Gryphon (forgot the model) driving the Magico M6. However this time, the bass was a bit slow and I asked for a piano recording which confirmed my thinking. Dealer then replaced the Gryphon with a Constellation amp and the bass went much faster. Hope you don't mind me saying so.
Although SS amps differ, I have noticed one phenomenon of SS users usually playing very loud but don't realize the sound gets uptight and actually tonal quality changed for the worse. Yes ears differ and perhaps mine are geared towards tubes, but the ART300 don't change when pushed and you still enjoy all the sweetness of strings, phenomenal soundstage, human voices with every change in tone and dynamics, without a slight change in tonal quality.
My guess is you may get slightly better bass with SS on your X1 (but not far better than the ART300), but boy you'll lose quite a bit on the midrange and highs.