I don't know about the other headphone "surround" modes, but Dolby Headphone will work with 5.1 or 2 channels (or even mono). With 5.1, the channels will sound separated, with the front channels having the illusion of being in front of you rather than inside your head, and the surrounds at the sides. With a 2-channel track, those front channels work the same way. It won't take a 2-channel track and make it sound as if it's all around you (as I suspect some of the other modes may do).
It won't fool you or anything, but it is kind of nice.