I’d personally go for a bit more power than a Zen, but you don’t need much. If these are your first high efficiency speakers be aware that a quiet amp is just as important as a good sounding one, the speakers will find any hiss or hum present. Have a good read of Stereophile as one of the columnists, Art Dudley I think, had a pair of Valencias and loved them. He used crazy expensive Shindo amps though.