I have heard two of the quietest tube amps recently. A Music Reference RM 10 II and a pair of Audio Mirror Eargasm monoblocks. Putting my ear next to my LaScalas with either of these amps powered up would fool you into thinking they were turned off.
Horns are notorious for revealing any shortcoming in upstream electronics. Horror stories of earbleeding experiences with horns are usually just that, mismatched components.