I just read your post above. And I interpret you as basically saying what you attacked me for stating:
'Volume has nothing to do with it'
A £50 fiio (or even a £25 behringer portable amp) and a £2000 Woo amp can both get the hd800/T1's to the same volumes decibels (measured by a DB meter), until one has to stop turning the volume up to save from hearing damage.
I believe that one is superior sound wise to the other, yet volume wise, they're both do the same thing. Clearly therefore volume has nothing to do with how they sound.
Sure, volume matters. If doesn't appear that you understand the science behind this. If one wants to listen to an amp at a higher SPL than the amp can perform without starting to distort heavily then you have a volume problem. That's the first thing you have to figure out when buying an amp. The rest is inconsequential if the amp is distorting because it has reached it's limits. Doesn't matter whether the amp has high SQ because it has a .001 THD at normal operating. Doesn't matter if it has zero channel bleed. Doesn't matter if the amp has a really low S/N threshold of say 120 db. None of that matters once an amp is reaching its limits because the distortion will be audible at frequencies where the amp is being pushed by the source material. Since the sensitivity of the T50RP is not that great, this the first thing one has to worry about.
Now the problem with the £50 fiio is that it will not be able to properly drive an HD800 because of the impedance swings, which will throw off its frequency response. But that doesn't seem to be an issue here with the T50RPs. That headphone is not relevant to this discussion.