Because of the universal praise of these units, I jumped at the chance when a friend offered me one in excellent condition with a small collection of tubes, for $80. Now, I've only had mine for a week, and have only tried akg k240, and t50rp mk2 on them. I've also only tried the GE jan5654, and russian voshkod on them. But so far, I'm not a fan. I like the power, which it has an abundance of, especially compared to the chi-fi max9722 based amp I was using (130mw / channel). The tubes definitely do something, the SQ changes noticeably with the tube changes, but to me it just seems like they're messing with the reverb. The unit picks up interference from nearby wireless devices, but it's not too bad long as you don't keep devices right next to it. The heat is excessive for a hybrid design, you'd swear it was actually class A after using it for over an hour. Overall, it's a really well built distortion device, with good driving power. I would actually really like to try out this amp without the tubes portions.