Cary SLP-03 Premium Tube Upgrade

Need some input please. Recently added a Cary SLP-03 feeding a solid state amp. I was wondering if a tube upgrade kit is worthwhile. I have no idea about tubes, this is my first. Any input on brand is appreciate. Thanx in advance.
These links are informative and should be helpful,

Personally, I don't have any experience comparing different 12AU7's.
As a Cary dealer, I feel that the 03 is very good preamp in stock form(especially at it's current price point). However, it will really come alive with a little tube rolling.

I've had great luck with Mullards and RCA's. Do a quick little search online and you should be able to find several different great options depending on what type of sound you would like to end up with.
Thanx, Gold...nice lil preamp. I'm guessing tubes are like power cords, interconnects, & speaker cables. Trial and error until you find that sound you're looking for?
Correct. You will hear differences b/t tubes.