Hi Brian, your right. I have not heard the Tube Research Preamp, you know I've had the amps. Sedond, I have zero experience with the Melos preamp, so I will not compare. As far as the comments about the Viva by Aaudio@home.com, the Viva is what I sold to buy the Callisto. After some of my friends heard the change, their Viva Linea is for sale too. Please see Audiogon Classified if you want a Viva Linea in excellent condition at great price.