I think Stax earspeakers take more speaker amp -like signals than headphone amp -like signals. I don't remember who, but I think someone has their faux srd7 set up as basically a pass-through (so basically the only thing it's doing is creating the stator voltage). That said, I don't think the Stax earspeakers present a pleasant 8 ohm or 4 ohm load, so the real boxes may actually accomodate for that. I can't imagine what else they'd be doing, other than the switching function. So as long as your amp can drive an unpleasant load, it should be fine.
Someone who knows moar bettr please feel free to call me on talking out of my ass.