I'm using the HE-6SE v2 with it and I personally find the mid-bass to be nicely flat (coming from the HD-650) but the sub-bass to be more rolled off than I would like. The latter is just something about the HE-6SE v2 itself, because when I lift the pads a centimeter or two away from my ears, the sub-bass becomes thunderous and very impressive, although the mids then recess due to the distance and lack of seal. I haven't done any pad swaps or other modifications yet. I briefly tried it with no grills, but it sounded a little too diffuse for my preferences. It's almost as if the bass reflections are cancelling themselves out with the stock pads, or they just need more distance to propagate properly; i'm not sure which. Also, I think another thing related to the amp may be that if sub-bass frequencies are sufficiently low distortion, then they may not be audible. Certain amounts of bass distortion can be perceived as increasing the quantity due to added harmonic energy