I finally have mine! I drove to pick it up since I was too impatient to wait for shipping
Was hard to focus on the road on the way back since all I wanted to do is tear open the package and start playing with the M8.
I have only had a short listen with my DT660s, but so far everything I had hoped for with this pairing has been spot on. Compared to my Nuforce HDP, I do feel like I am getting a better soundstage with better positioning of instruments. The first notch on the bass boost is what the doctor ordered to take these surprising headphones from fantastic for classical to quite good as an all rounder. I might end up keeping these and sell off my modded T50RPs now.
Will report back as I test with HD800 and my IEMs.