Schiit Jotunheim Measurements

Interesting question! Anyone?

 

First of all: gear that measures superbly wrt distortion(s) is not guaranteed 'shrill' free. Plenty of crappy sounding sublimely measuring gear out there.

Such distortion measurements do not show time domain gremlins (phase problems) and give limited view on dynamic performance.
I personally wouldn't say Jot with HD800 is 'oh so shrilly'. No more than some other gear, but certainly different kind of 'shrill'.
More like a little bit shrilly and it adds up to HD800's nature. It depends on source quite a bit as well.
It's quite alright while driven with a Soekris dac. A bit edgy from Yggdrasil and not that great with it's inside dac for HD800.
The Jot has subjectively blazing transients, this is why 'features' in highs are more pronounced.

Probably only Schiit knows the answer to that. Or not. It surely needs deep knowledge of the circuit and some serious man hours into testing.