You get double the output current, and the parallel connection probably reduces distortion too, as it does in all-discrete power amps: Cordell's textbook on Charts 3.6 thru 3.8 (pp. 69-73).
That'd be my expectation as well.
Short circuit output current is even 490mA, but I doubt I will ever come in this region. I have a demanding, but not very demanding pair of headphones.
True. Don't expect linear operation there, though.
Tom