The Sennheiser headsets are fixed to the suite, and cannot (discreetly) be removed. You are certainly welcome to use your own headsets, there is a single pronged plug below the inseat power outlet. Always questioned the decision to use fixed headsets. On my last domestic cycle, saw 4 customers seated in Y/C using the former International J/C (property of Air Canada) headsets. Hmmm.
I am not judging...really, I'm not.