I too love crossfeed. I use it all the time, and built it into my cmoy amp. I have a perspective switch installed, so I can make it more crossfeed, or less crossfeed, or bypass crossfeed. The idea of trying to keep the music as clean and unproccessed as possible is a valiant one, and one I agree with for the most part, but headphones are limited by the fact that while engineering a mix, the recording engineer is listening to two nearfield monitors in a stereo configuration. He/she is mixing all the channels on the board, AND they are 'mixing' the natural crossfeed 'pseudo' channels. They are expecting you to hear those pseudo channels of acoustic crossfeed. When you listen to headphones, its like you have just removed two channels from the original engineer's recording. You are hearing the WRONG mix! Now, this isn't necessarily a problem, the increased detail and precision of headphones makes them attractive for critical music listening, but it can be hard to do without those two channels. Crossfeed is a simplistic, but reasonably effective, way of preproducing those two channels that we lose by wearing our speakers on our heads, instead of putting them out in front of us.
If you are very used to listening to headphones without crossfeed, you may have 'adjusted' to the headphone sound, and won't like the crossfeed. Some headphones benefit more from crossfeed than others. Some ears just like it better than others.
I don't believe that it detracts from the sound or lowers the sound quality. I believe that it improves the quality of my headphone listening. I suggest that everyone give crossfeed an honest try, and see how they like it, then they can decide if they want to keep using it. Some people just won't like it, and they can stop using it, and go back to their unprocessed world. Some people will like it on everything! others, like me, will like it more on some things, and less on others, and adjust their settings as desired.
Peace,
phidauex