Recently, I found a rather advanced EQ plug-in for Winamp called Nevi. The website it points to is long gone, but the software remains. Just to play around, I downloaded some frequency charts for my ear ware.
I found that you could achieve a reasonable approximation of correction to the errant frequency response of a given listening device.
Just invert what you see as the deficiencies in the response, and apply the reverse. I did find that if you do that exactly, the frequency response sounds entirely too bright. Of course, I remember this from decades ago research where testers did the very same thing. BUT, after taming that brightness, maybe, just maybe the Sennheiser HD700 doesn't suck so much.
The cool thing is that this software EQ add-on to Winamp claims a 250 band adjustment range. I was able to match the deficiencies of just the measured FR of a given device. Like I stated earlier, the result is exceeding bright, but after taming, definitely closer to flat that the listening device by itself.
The reason I post this is to seek opinions from anyone else whose played with this plug-in.