You said the 560 has a different tonality? I recall people describing them as more neutral, is that correct? Would you consider them a good upgrade over the 400i? Besides them leaning more neutral, how would you compare the two personally?
Yes to me HE-560 is tuned more neutral in comparison to HE-400i. I would rate it as fairly neutral headphone, although sometimes with bright recordings it may sound a bit aggressive in lower treble (around 4-5 kHz). To me HE-560 is only modest upgrade from HE-400i in sound quality. But it also depends which genres you listen the most and what kind of tonality you prefer. In my opinion with rock, pop or metal HE-560 sounds only marginally better ,if better at all, because HE-560 midrange sounds thinner and drier in comparison to HE-400i, which on the other hand sounds beefier in mids and bass giving vocals better weight and providing stronger bass slam. Modern pop , rock or metal is also usually awfully compressed/brickwalled so HE-560 advantage in better dynamic range or extension on both ends does not play such significant role. On the other side HE-560 strenghts and better technicalities would certainly show up in (especially well recorded) classical, jazz, blues or contemporary music where HE-560 better staging, airiness, bass/treble extension, slightly better layering and reproduction of microdetail would be preferable.
Yes, the 560s would be more neutral (most easy to hear in the lower frequencies) and they are more micro-detailed everywhere, but the treble spike many people complain about with the 560 is worth taking into account. I owned a 560 for a year with extremely good amplification and yes it is an upgrade in pure objective terms but as you know this is very subjective. If you have decent amplification, like a little less, but more detailed, deeper sub-bass, then the 560 is worth considering. The 400i gets you most of the way there mind you, and it is a more forgiving signature overall.
I basically agree with Sonic Defender here. HE-400i is definitely more forgiving of poorer recordings and also a bit less prone to sibilance.