Which serial number HD800 have you heard for comparison ?
K812 has noticeably more bass presence and better bass tightness/accuracy than more than early serial HD800's. And slightly more, but also smoother/less grainy as compared to newer serial HD800's.
Looking at graphs, I was worried both my T90 and K812 would have excessive bass, prior to actually hearing them. Upon receiving them, neither have excessive bass for classical, but i feel the K812 has just slightly too much bass for my tastes, when listening to most modern music, from say 2008 on forward, as engineering across all genres has specifically dialed it up as of late.
thought the kibosh had been put on the rumour about sennheiser changing the fr of the hd800