A Tale of Two Amps
"It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, we had everything before us, we had nothing before us, we were all going direct to Heaven, we were all going direct the other way—in short, the period was so far like the present period, that some of its noisiest authorities insisted on its being received, for good or for evil, in the superlative degree of comparison only"
A member of our audiophile group has the Nola KO's (90 dB) with the Ultravalve and they sound great together, but for fun I brought my Synergy 450 over for one of our meetings. The Nola's impedance ranges from 8 ohms average / 4 ohm min. so the Synergy could have been putting out 900 watts depending on the music. Overkill? No way, the headroom was palpable.
At low volumes the sound of the two amps was very close but turn it up and the Synergy 450 had a take no prisoners lock on the bass compared to the Ultravalve. So it all depends what you listen to, how loud, and where you live. The Synergy 240 with the Zu would get you kicked out of an apartment.