I have been playing with Roon's crossfeed (in their DSP engine) with headphones and I like it (at least on some recordings) overall, though it has a "sound" obviously.
I noticed that miniDSP is coming out (shipping end of May 2017) with a portable Headphone DAC/AMP with a few built in DSP features (EQ, crossfeed, etc.):
https://www.minidsp.com/products/dsp-headphone-amp/ha-dsp