I just listened to too many headphones and headphone amps in one day. But, the two that I am remembering as something special were the SR-009S Signature Electrostatic Earspeaker and the RAAL Requisite.
The SR-009S was powered by a Blue Hawaii and the RAAL by the VM-1a. Amazing head fi experiences.
I’ve always fancied a listen to a decent Stax pair of headphones. I’m concerned it would trigger an impulse purchase though. I’ve not long bought new cans and I don’t need…
Who am I kidding 
When I went headphone shopping a few years ago, I avoided listening to anything over my budget (about £1600 - GBP) for that very reason. The dealer had all the Stax range and energisers available to listen to and he asked if I wanted to listen to them.
I have the blue hawaii and both Stax and Audeze headphones. I have already posted pics in the headphone thread so won’t cross post here.
I heard the Raal, sr1b and they were very uncomfortable and lacked bass, the ca1 were better balanced and more comfortable.
Both Driven by vm1a amp which I noted while at the dealer the volume pot was already quite noisy, so not sure if it was a one off or something to worry about.