For headphones, the ribbon earspeaker idea I've been kicking around. I'm going to finish off a few other projects then give them a try. I've been obsessed with ribbons for years. Always preferred them to electrostats, but there aren't any ribbon headphones. The Ergo AMT is very close, but I want to try my hand at a pure ribbon. I think it is possible to adapt a ribbon microphone setup into a K-1000 style headphone. I'm going to try it.
For amps, the 45-based transformer coupled amp I've been gathering parts for. I have the 45 tubes and just received a pair of Sowter headphone transformers with multiple taps. I'm putting in a switch so you can select output impedance based on the headphones you want to use. I need to put in an order for the power, filament and output transformers with Electra-Print.
Still plan to get around to building an electrostatic amp and picking up either the Omega II or 4070.
I have yet to hear it.
Its highly possible that I have the Holy Grail headphone in the Stax SR-007BL, but I have never heard the Holy Grail in amplification for it. Of what's out there it may be the HeadAmp KGBH SE.
A well driven AKG K1000 is certainly up there as well.