Can't speak for the Mk2 but I had original SE-100's and currently Plinius SA-100 mkIII. The Monarchy had nowhere near the bass and power with some speaker combinations but, apparently, that's been improved for the Mk2. Still, you're comparing 52lbs versus 75. The Monarchy also had a slight upper-mid/lower treble peak that I felt accentuated the soundstaging to the point of being a bit artificial. It can be a sweet amp with the right speakers. The Plinius, on the other hand, is laid back and understated, more than some prefer. It's not trying to impress despite it's capability.
Comparing new to used isn't fair. A new SA-103 is several times the price as the Monarchy's.
Comparing new to used isn't fair. A new SA-103 is several times the price as the Monarchy's.