First of all, I am a big headphone guy - have multiple pairs of high end headphones (willing to bet on a whole different level than what the op is using) to include heavily modded orthodynamic/orthostatic as well as traditional.
Typically I use these
with a dedicated pre-amp and tube amp setup
so I am very familiar with headphones and they simply are not the same as traditional SS set-ups. First of all SPL vary greatly. By moving or adjusting headphones even a few millimeters on the ears you can radically change the sound. Properties such as soundstage, localization, Bass levels are dramatically affected as a result. Also the size of the drivers on headphones makes it very difficult to accurately reproduce low frequencies as they simply can not move enogh air.
Here is another (and the main reason) that surround sound systems differ from headphones. As distance from the origination of the sound to the listener's ears increases the properties of the sound waves change both in intensity and frequency (a small part of the doppler effect). Headphones have no way to account for this. Surround sounds set-ups have adjustable delays to account for the distances and positioning of speakers. Speakers 5 ft from a listening position have a different setting than ones 20 ft away etc. Headphones have no way to account for this as they have no way to determine the distance from a listener that a sound originated so they do the best they can to approximate what it would be like at the listening plane. If hearing strictly digital it would be different but sound waves are analog and overlap adding and subtracting to wave propagation based on distance from point source. Once again these are things headphones can't accurately reproduce or account for. As you go up in Headphone quality the approximation can get better but never exact. This is one of the reasons that when you wear headphones the sound often seems as if it is originating inside your head even with directional clues.