I always come across this, he560 is similar to hd800, how can that be? The guy next to me in the office have a hd800 and i have a he560, for me they are not similar when i am switching between the two. Either i have a bad he560 or he has a bad hd800 or we both have bad ears lol.
no, I think you can definitely pick up on differences between the headphones. especially if you guys are using different amplifiers/dacs.
for me, the things that stuck out to me was they have differing bass presentations (he-560 have more linear bass extension down to the sub-bass while the hd800 has a bit of a relative mid-bass emphasis in comparison). For mids, the HD800 has a bit warmer sensation with its more lower mid focus, but the HE-560 sounds like the relatively warmer headphone overall with the HD800 sounding subtly brighter overall in comparison. For treble tuning, they actually have peaks in similar regions of the highs, but to different degrees. The HE-560's lower treble (esp 6 kHz peak) is much more emphasized compared to the hd-800s treble presentation which focuses a lot more on the upper treble. HE-560 sounds to me to have a stronger sense of impact (harder-hitting like @Wildcatsare1 stated) as well. the HD800's soundstage is wider and gives a more "open" and "airy" sensation due to its high treble. The HD800's performance seems to vary more with different amplifiers, so finding a good amplifier "synergy" match appears to be a bit more important for them. Less highly recommended mid-tier amp options for the HD800 than the HE-560 from what I've seen.
however, if comparing relatively to many other flagship headphones, the HE-560 & HD800 are definitely more similar than different. I know @Wildcatsare1 has both right now as a pair, but most other folks usually just find one of them to match their preferences better & picks between the HE-5560 vs HD800 rather than buying both as complimentary headphones.