My D18 is on the warmer side but I wouldn't call it dark and it sounds fine. The main concern with the Mjolnir is as long as your dac is good then it should be fine. The Mjolnir while it does tip towards the more aggressive side reveals what is lacking in the dac if you have the proper headphones of course. However judging from your headphones they probably are good enough although my preference for the HE6 would not be the Mjolnir but the pair does sound quite good.
Also that balanced amp he has selling is interesting. Not many of those amps come up and definitely not balanced. I never got a hold of them but don't really need one now. The only amp I can think of I would buy right now is if a GS-X made it to the FS. One came up a few weeks ago and don't think that's happening again for a very long time.
I was very impressed with the Mjolnir when I heard it because of that aggressive sound. The detail retrieval was just so refined, and the sound decay was really impressive. Of course I only got to hear it at a meet when it was being first debuted so there was a line and I didn't want to take too much time. Does it do OK with so-so (e.g. mainstream) recordings? One problem I have with the HE-6 is that it's hard to just hit shuffle and listen. Those headphones just rip apart anything that isn't well recorded.
I've been trying to scrap around and find any information on that darned unit with very little to no luck. All the comments are for SE, and from 2008 or so.
Keeping things relevant to the Matrix. A concern I have with the Mjolnir is that some people now talk about the "three blob" sound stage. I think the Matrix has a good "music upfront and dissipates to the side" type sound. Any comparison on the sound stage? Not to be too demanding :) Just any thoughts you have when you have some time.