Hi Steve, I'm currently driving my amps directly with my Wadia 581, as I'm between preamps. I think that it had a better sound overall with the Audio Research Reference 3 preamp that I had. I'm waiting for my new Pass Labs X 0.2 preamp to arrive. However, my Wadia 581 isn't completely broken in. It has 680 hours on it. Full breakin is 750-800 hours and there is sapposed to be a marked change for the better around 750 hours. Also, the Wadia 581's volume control hasn't been up any higher than "73" driving the amps directly. I ran it on "100" with a preamp. The Wadia 581 sounds best between "85" and "100"-max. That said, I'm getting a low noisefloor with great dynamics and air. It is very clear with the best texture of instruments that I have heard in my system. The downside, since not having a preamp in the chain, is that bass, while being full and dynamic, isn't as controlled and precise as it was with a preamp. I'll know more once the Wadia and Pass are fully broken in. I do think that the voltage output can be adjusted. I'll post again as everything breaks in. I should receive the X 0.2 this coming Wednesday. Good luck. Best regards, Stan