I just published the design of a DIY hybrid headphone amp using the new Korg Nutube 6P1.
It's a lot like the original "Millett Hybrid" that I published 15 years ago. Instead of an old car radio tube, though, this one uses the new Korg Nutube. The Nutube has been popular with DIYers in Japan since it started shipping at the end of last year, but so far I haven't seen it a lot outside Japan.
Like the original Millett hybrid, the whole thing runs off of a 24V power supply, so it's safe. I used OPA551 opamps to drive the headphones, but you can use others as well.
You can find all the details on my web page, at http://www.pmillett.com/nuhybrid.html