Let's organize an alphabetical list of headphone amps (heard and approved by many) that are known to be some of the very best amps for the HD800, cost-no-object. Anyone can chime in and update the list, even delete what's already there if you don't agree, but only as long as you've actually heard the amp and compared it with others.
And please, let's not argue over tubes vs. transistor here. As long as it sounds heavenly with the HD800, everything's good.
VALVE
- Allnic Audio HPA5000
- Decware CSP2+ (soon to be upgraded to 3)
- DNA Stratus
- E.A.R. HP4
- Eddie Current Zana Deux SE
- EternalArts OTL-KHV
- Woo Audio WA22
SOLID-STATE
- AMB B22
- Bakoon HPA-21
- HeadAmp GS-X mk2
- Luxman P-1u
- SPL Phonitor
- Sugden Masterclass HA-4
- Violectric V200
Disclaimer: To be honest, I didn't listen to all of the amps I listed above (GS-X mk2, for example, though I'd really like to hear it with the HD800 someday). I added several amps I haven't heard but received a lot of praise from respected members at Head-Fi and other sources. So far, the best tube amp I've heard was the HPA5000 ($5K), and the best solid-state was HPA-21 ($3K).