I'm in agreement with soix, atmosphere and others. With the Monitor Gold 300s, for sure, it wouldn't be good to match with a SET amp or even a low to mid powered ultra-linear tube amp
If looking for the romance, and warmth of tubes (as nice of a pre that the Benchmark is) you might consider going to a tubed pre matched with a smooth 100W+ SS power amp.
While the tubes in a pre. tend to hold up and last a long time even when driving 4 ohm speakers, the tubes in mid to low powered power amps, not so well.
I loved the sound of of tubes with my Maggies, but have gone through two sets of KT-120 tubes in the past 2 years, not to mention the trouble of replacing fuses and resistors.
I went back to my old reliable Audible Illusions tubed pre, driving a 200/400 watt SS power amp and am most happy.