Someone I know preferred the Dartzeel pre to the Shindo Giscours pre into his Shindo amps
I must admit I share Madfloyds experience
I used esoteric pre with big el34 tube amps with valve rectification and separate power supply for driver sections
The extremes were much better presented
The fact thus pre can also swing enormous voltages like valve pres a la AR 6 and 10 gives both synergy and great extension/ dynamics
It's the opposite of what's often said ie valve pre ss amps
However I found it a very natural sound
All instruments sound more true to life
El 34 is known for its midrange
The esoteric seems to add superb highs, and explosive bass to the mix ! YMMV