The Studio Series two π tower and Theater Series four π are the most popular speakers for people with tube amps. I really like the cornerhorns, so the seven π is one that I would strongly suggest. While the impedance at resonance of the Professional Series is a little higher than what I generally recommend for SET amps, some of 'em do just fine with these speakers. If your amp is one that isn't terribly sensitive to load, you might enjoy the Professional Series four π or seven π speakers, or better still, the Audiophile Series seven π-18. I'm enjoying a pair of Professional Series π Speakers on a pair of 2 watt SET amps, and I'm absolutely loving it.