I have a pair of Omen Defs and every amp I have thrown at it sounds really good. Even an old Pioneer Elite Receiver that I had used for a bit in between purchases. The only thing I would caution with high sensitivity speakers (like the Zu's) is super high output amps paired with the preamps. Tube hiss will be much more of a factor. Even the newer McIntosh "hybrid" integrated may have a bit too much gain for the Zu's
