The old Gigaset certainly works with Dect. If a Jabra headset could already be connected wirelessly, then this should also work with a new DECT-capable headset.

I think the old Gigaset had Bluetooth built in - unfortunately the E560HX does not, and so there are no wireless headsets that can be used with the E560HX. At best, you can connect (pair) a DECT headset that is independent of the handset with the base station/router, but this has nothing to do directly with the E560HX.