they work well in large rooms (i'd generally characterize them as sounding larger than they look). they're pretty "full" sounding, so try not to place them too close to the front walls (might cause bass overload), then again, each room is different so it's best to experiment.
in terms of amps, both 300b & 211 (single or parallel) are sufficient to drive the Eufrodites' (i'm using the Kondo Ongaku, but hv also heard them with Kondo Kegon). i've also tried them with SS amps, but feel a good SET amp - esp. one that sounds a little "lively" - brings out the best in these speakers. hope that was helpful.