The HE-560? The HD800, Stax, HD600, and DT880 (all outstanding open-back headphones for classical) have less sub-bass than the HE-560, which hits incredibly deep but only when called for. They are also extraordinarily fast headphones, not matching the Stax but spinning circles around my HE-500 and surpassing my HD800. Whether sub-bass is important for classical is kind of subjective. For me, I consider it less important than for other genres, but I could see why it is important. I do not feel the HE-560 is lacking sub-bass I require from my listening.
The HE-560's nearest competitor is the Ether so comparisons between the two should be of high interest to anyone considering a planar at this price-point. Both of these have been compared to the HD800 as well.
Of the headphones I have heard for an extended period using my own gear and sources, the HD800, HE560, and HD600 are my top choices for classical--each appeal to a different price-point. The Beyer is very close though, a really magnificent headphone for classical. I admittedly tend to value transient speed, dynamics, imaging, soundstage, and tonal accuracy above everything for classical--all of which I feel the HE-560 delivers in spades. Like every headphone, though, it too has its flaws