Mjolnir is definitely not on the warm side. There's an inherent upward tilt with the circlotron topology.
That comparison makes me think the Emo is very bright. What DAC and headphones are you using?
Well, double amping is something that's never recommended, but the best way to determine what sounds best is to adjust with your ears.
I don't know what technology is behind the Mjolnir but I do know my ears. If it's a unit to unit difference that I experienced then sure. But I don't seem to be alone in thinking that the Mjolnir is slightly warmer than Emotiva. And no, the Motiva is not bright even when compared directly to a well known tube amp that is very neutral and costs 14x more.
And saying double amping is something that's never recommended is a little untrue also. When needed in certain situations, it is indeed recommended with a big "proceed with extreme caution". I used to double amp to drive subs in live performance for venues in which I showed up and the amps were inadequate to drive the subs.