I own an Usher R1.5. power amp.They are very good and sound rich and meaty with very good timbre.They also image very well.Lots of other amps have come and gone but that has stayed because it just sounds natural and unforced and has none of the usual "solid state glare "which tends to cause listener fatigue.
The treble is as good as the preamp you use and if that combination is right is of very high quality.It sounds superb with my Supratek preamps.It seems to work best with high gain preamps.The Usher preamp is not a great match although it can sound excellent with other power amps.