iampan, impedance also plays role between making a regular spec speaker and (I use regular very lightly) headphones compatible. They work on same principles but are very differently specked out. You would also need an additional line level amp to help drive the speakers from a headphone output especially using a headphone output from a computer (volts maybe amps none). The axis of the output of the speaker would play small to no role at all. Only because I imagine it is close proximity and not very far away and off to one side. lightspeed needs to push some air although it would make sense that a high freq. speaker would make it some what easier to hear. If quality plays no role then it really doesn't matter.
I forgot the most important issue your talking about a wireless headphone application and that in itself is totally another problem.

I thought maybe RadioShack still made some that weren't that expensive for use like speakers on your patio or something. The same for the larger home improvement stores.
raybe