And I already thought the Head-Fi forum have finally outlived this misconception...
...because the HD 800 is one of the easiest loads, electrically speaking: high efficency, high impedance. The Hugo has more than enough power to drive it. What you actually mean is that the HD 800 needs a
full and warm sounding amp to compensate for its brightish and leanish characteristic. Most tube amps will certainly fulfill this precondition, also some solid-state amps. But the coloration comes at a price: reduced resolution and missing microdetail.
I have lived quite a while with the Hugo/HD 800 combo and liked it very much, way better than with any of my amps switched in between – but I wasn't relying on the «factory setting»: Firstly I installed some
dampening material into the ear cups (which already removed some of the high-frequency excess), secondly I used an equalizer to flatten the perceived amplitude response by ear. The resulting curve looks like this:
Or more precisely: that's the projected curve for an
unmodified HD 800. If you try it, you will be surprised how good the HD 800 can sound through a neutral, ultra-transparent amp, not to speak of an ultra-reveiling source like the Hugo.
BTW, the so-called critical load characteristic in the form of the impedance hump at the resonance frequency is a red herring: The Hugo can even drive loads as high as 100,000 Ω – that's the case if you attach an amp to it. Moreover, the «critical» 100 Hz region is where the HD 800 has a particularly high efficiency, which means low current flow anyway.
Don't get me wrong: I'm all for tayloring the sound to the own sonic ideal, and not everyone is an audio purist who wants the most honest sound he/she can get. And I certainly like tube sound myself. It's just that I think even if you want some coloration now and then or here and there, you're better off to use an equalizer instead of amplifier colorations. This with the goal of maximum musicality (yes, absolutely!) and enjoyment. Also, with the amplifier route you would need different headphone amps for different headphones... and still the amp wouldn't really care for the headphone's flaws (e.g. limited bandwidth), just make them less obvious.