Don't know if you made your purchase or not (it has been couple of month since your original question) but I can fully agree with Rgd about tubes in a preamp. Not all of them are warm. Something like Conrad-Johnson PV-14L would be one of the warmest and smoothest. It has only couple of inexpensive tubes and it is reliable. You need it because your source is not the warmest among CD players (I would call Sony players "grey" in sound/color category), detailed with leaning toward clean sound. You will love it with the "right" tube preamp, as Rgd said.
Godd luck.
Godd luck.