The Music Reference RM200 is a fully balanced 100 wpc power amplifier with a transistor input stage and tube rectifier and output stages. It is my favorite amplifier with the WP7s, which present a load that is very similar to the WP5.1s. It is a particularly good match with these speakers because it can deal effectively with low impedance loads, and can make the Puppies behave. The amp is attractive, built to last, and can be had for anywhere between $2.5k to $1.7k on the used market.