I use Atma-Sphere, the M-60 Mk II.2. These are a revelation. Their reproduction of dynamics, high frequencies, timbre, timing, bass, control is amazing. These are easily the most fluid, grain-free tube amps I ever heard. Super fast, clean and clear, natural and balanced for the whole spectrum, they are superb. I believe, I had a mesmerized look in my face, when I first listened to them. There is everything I hear from my Pass amps AND MORE. They give me every detail with lots of air, combined with brutal power in the bottom without being euphonic linked with stunning speed and transparency. In any case, the sound these amps produce is almost frighteningly real - clean, open, "air", wide soundstage, unbelievable detail - it's all there and then some. And : there is NO "warmth" or other tube-related anomalies - just clean, accurate musical amplification.