My own counterpoint to this is, the mojo amp will pass along the rest of your audio chain to the 800's And yes the 800's can be 'bright', but they can be toned down.
In my pairing of the 800's and the mojo, the inner details and resolution and especially the bass extension are marvelous.
I think the Mjolnir is a first-rate amp, and I'm sure you're enjoying it with your modded HD800s. I agree that the HD800s can sound very neutral with the right chain feeding it. That being said, I think the HD800 (unmodded) is bright out of the G/M chain, and I don't see many HD800 owners (or others with headphones that can run bright) preferring the Mjolnir. We all have our preferred voicing, and with head-fi--you only have to please an audience of one.