What are your opinions of Sim Audio amplifiers?

Moon by Simaudio builds outstanding gear. I have owned their CD Transport, DAC'S, Integrated, Preamps and Amps. Nice gear.
What are you using for a pre?

I am using Pass Labs XP10 for pre-amp.

I owned W6 monoblocks paired with Dynaudio C4's more than a decade ago.   I found them very underwhelming and sold them within a few weeks.  Not impressed. 

@andy2 it is not your preamp that’s for sure…

The older Sim gear when they made the transition from Celeste to Moon, like your W3, was really good, a great value, and looked cool. Today their stuff still sounds great but the retail prices are getting out of control ie the 6 figure 888 flagship mono amps. Tech in the audio world (outside of digital) isn't really advancing that quickly.  You could even argue that we might be going backwards when you consider turntables and tube amps. Changes between model generations amount to tweaks rather then leaps which makes the price jumps hard to justify-  ex. the W5 introduced in the late 90's was $4800, its current equivalent the 860a retails for 14k.  Adjusting for inflation the W5 would be about $7,500 nearly half of it's contemporary.  Place the two side by side and you will probably discern a marginal improvement assuming you prefer the 860 which is no guarantee in a blind test.  It's not just Sim though, lots of manufacturers have engaged in rampant price escalation over the years.  Its hard to blame them when  audiophiles go through cognitive dissonance trying to pick apart minute subjective differences and end up picking the more expensive component.