As a former Xono owner and former ARC PH7 owner I'll speculate you are not hearing all that your upstream front end is delivering. There is a comparison of the two in this review. The Ref Phono 2 is a significant step up from both and you're right, it is very quiet.
As a solid state unit, the Xono may have a wee bit more crispness on the low frequency leading edge, but if there is a difference it is slight. The RP2 has better tonal definition and is more micro-dynamically adept in the lower frequencies. Otherwise the Ref Phono 2 is superior to the Xono in every other attribute and not by a small margin - and it should be at ~3x the cost. I have not yet heard the new PH8, but early reports suggest it is closer to the Ref Phono 2 than to the PH7 - so something else to consider. I like the Xono; it is quiet, fast, and flexible, but, imo, either ARC phonostage will be a considerable step up.
As a solid state unit, the Xono may have a wee bit more crispness on the low frequency leading edge, but if there is a difference it is slight. The RP2 has better tonal definition and is more micro-dynamically adept in the lower frequencies. Otherwise the Ref Phono 2 is superior to the Xono in every other attribute and not by a small margin - and it should be at ~3x the cost. I have not yet heard the new PH8, but early reports suggest it is closer to the Ref Phono 2 than to the PH7 - so something else to consider. I like the Xono; it is quiet, fast, and flexible, but, imo, either ARC phonostage will be a considerable step up.