Unfortunately you're mistaken.

I think you're confusing "Single Ended" with "Single Entry".

Single Entry != Single Ended

As long as the headphones are not wired internally with the grounds tied together (Which in this case the HD560S is not), there's nothing preventing a single entry headphone from being ran balanced.

The only thing making the HD560s Single ended (unbalanced) is the cable / source. If you have the right connector (a 4 pole locking connector that fits the headphone), and wire it right, you're in balanced capable territory, just need a balanced source and the right connector going to the source.

Other examples of balanced capable "Single Entry" headphones would be the Fostex T60RPs, Modhouse's Balanced Argons, Hifiman DEVA, Beyerdynamic DT177X GOs, The new Hifiman headphones with the ridiculous cups (Can't think of the name, but boy can I picture the hideous things, they're a metallic red) that can take a balanced single entry connection etc.

Hope that info helps / makes sense. As someone else linked elsewhere in the thread, Sennheiser themselves have confirmed these headphones are balanced capable. That way you don't even need to believe / trust me.