Funny thing.
Actually, E12A has very good regarded op-amps, muses02. Hugo has no op-amps. My understanding of these is limited, and come as it may, I think that filtering the signal from hugo at 3Kohm literally filters the hiss down to a below noise floor level. This might make E12A sound like it looses some details, but it actually does not.
To note, E12A is a smooth amp, it does make treble less sibiland and less harsh.
Amps with lots of hiss tend to sound more energic and full of life, like E12 X5, Hugo, when E12A sounds very efortless, relaxed, like it is not giving a Fu about amping, it is easy for it.
Also, to note, I push the volume on my E12A down to 1-2 oclock, seetspot at 11-12, with ie800, because I lower the volume on X5, by having EQ on, and dropping all sliders to -6.
I am not sure if the lower hiss is worth it about adding more amping to hugo's signal. You can achieve a similar thing by adding a 150OHM plug in the signal path. Practically, high impedance makes hiss in-audible, as far as I noticed. Like hd650 or hd800 does not have hiss because of very high impedances. My ultrasone 64 ohm has lower hiss than ie8. With ie800 I like the sund better with E12A but I do not think that I hear hiss at all. I am not sure if I hear hiss or not.