yup that's it right there, the m2505.
For sound, it is super smooth and has a bit of softness but without the euphony or warmth you get from tubes. The tone is really SS like, transparent and clean but without the harshness and roughness you get from a typical (bad) SS sound. Bass is a bit boosted and adds a ton of impact and weight to a headphone's bass response. IMO it's neutral sounding or maybe ever so slightly south of neutral.
Detail is superb and the headphone output is powerful. It's not optimal for the he-6, but at vol levels where there's no distortion, the sound has weight, and the bass is still well driven. I can't wait to see how much better it gets once get the adapter so I can use the speaker output. It's headphone out is probably overkill for most other headphones. My hd 580 doesn't even go past 9 olcock.
As for cons, it does not really add anything (nor detract) to improve staging and dynamics, how good those aspects are will really depend on the recording, dac and headphones. It could use a bit more air to the sound however, but it's not dark or closed in by any means.
Also the vu meters are mesmerising, and the lights are perfect in terms of intensity (bright enough to be seen in the dark, but not so bright that it hurts the eyes or distracts you), the L/R gain pots could be smoother. But all the other pots give a very satisfying click.