I do not think you would plug the headphones into the speakers?
I would just plug them straight into you sound card. You would need a sound card with optical digital output, or if your card only have coax digital output you can get some converters to make them optical. Course you could always just connect it with analog inputs, but you will not get the DD signal. Not sure how much that matters, I never played with anytype of "surround" headphones.