I am happy to know people like the sound of HE-400 with classical music.
However, for me personally, it is still difficult to make a decision between HD6xx and HE400.
No need for that, just get both. Seriously, at the current price point of the $299, truly peanuts for this kind of performance, you should have both. Or get one first and then add the other later.
I'm listening to Chloe Hanslip with the London Symphony Orchestra as I type this. The real key is the Crack amp for this chain. And OMG is it good.