In hooking up my 300B SET amps to my Silverline SR17 monitors (89 db) I've found they can play at very conservative volumes, but the limits of headroom approaches rapidly as you increase the volume to more engaging levels of listening (for me this is around 85-95db, but my wife claims I'm hard of hearing). At those levels that combination renders some very audible distortion when pressed. I would definitely not depend on that combination as my system unless it were a bedroom system for occasional low-level listening, or perhaps a background system. Either of these applications seem to me like a waste of a good amp(s), as well as some outstanding speakers in the case of the SR17's. For an 8watt SET system I'd keep my minimum efficiency worth considering more like 94db to give you a more practical application of those amps. I've had pretty good results with 90db floorstanders, but ultimately I'd want a bit more for my 8 watts.
Marco
Marco