That is easy, none. Headphone listening gives a completely different balance and presentation than speakers, for example the room has no effect at all while with speakers it is the dominant factor. The two channels are totally separate unless you have a device to mix them while with speakers you always hear a mix. The headphones only have to move the small amount of air in your ear while the speakers have to drive the whole room.I have used Stax headphones to evaluate my system for 40 years now and I have yet to hear speakers, including electrostatics, which sound like them. You can try for a similar balance in the sound between the two, just don't expect too much.
