Three noteworthy amps, from my experience:
Benchmark HPA4 - maximum transparency and detail, clinical in its precision
Ampsandsound Bigger Ben - incredible musicality, a touch of warmth, lots of power
JDS Labs EL II - All-around solid performer at a budget price of $250
The Darkvoice 336SE OTL amp would be an interesting choice, haven't heard it but I imagine it'll have a distinct sound: alas, I've heard about quality control issues.
Benchmark HPA4 - maximum transparency and detail, clinical in its precision
Ampsandsound Bigger Ben - incredible musicality, a touch of warmth, lots of power
JDS Labs EL II - All-around solid performer at a budget price of $250
The Darkvoice 336SE OTL amp would be an interesting choice, haven't heard it but I imagine it'll have a distinct sound: alas, I've heard about quality control issues.