Andy, Roger Modjeski designed his Music Reference RM-200 tube amp specifically to deal with low-impedance loudspeakers. When they occasionally become available on the used market, they fetch around $2,000 for the original version, a grand more for the Mk.2. A pair of KT-88 tubes are used to create 100 watts (per channel), into all impedances. The RM-200 is a VERY unusual tube amp.
In his original review in Stereophile, Michael Fremer placed the amp in the mag's Class A Tube category, and in a follow-up review found the Mk.2 iteration to be an even better amp. It has remained his "moderately"-priced reference tube amp for over a decade, and he recently declared the RM-200 MK.2 to be one of his most-cherished hi-fi possessions.