I am not a fan of the JJ tubes but I would wait until you have many hours on the preamp so you can really judge what you want to improve by tube rolling.
musica bella tube preamp
I finally got my new musica bella lusso preamp a little over a week ago. Right out of the box it has a very nice sound to it. Compaired to my old ps audio solid state preamp the lusso has more weight to the music. It is very dynamic and has that emotional connection to the music. It really pulls the inner details from the recording and I know that people always say this, but I am hearing things in my recordings I didn't hear before. All the extra detail and it is still very smooth and never harsh. I have always read that tubes can run hot but this pre can be on for hours and still stays cool. I would like to do some tube rolling and when I asked the manufacture about tubes to try he said that he thought I should let it run for another 100 hours or so before changing anything. Do you think that I can do better with some nos tubes (JJ electronics are in the pre now).