The 40 seems to go very nicely even from my Rio Karma DAP. The 30 and 50 prefer more juice, though I have used both outdoors with the Karma. One day when I have the cash I'll get a 50RP to play with. The driver looks nice from a technical and design standpoint so I don't see why it shouldn't sound good too.
What are they, $70-80? I should be able to swing that one day.