It's ALL about the tubes. Characteristics will change dramatically with each change. Mullards are very good but very overpriced so don't go crazy. You're on the right track.
Tubes for Cary CD301
I just picked up this CDP and it has stock tubes. A poster on Audio Review suggests that Amperex 12AU7PQ for the voltage gain stage and Radiotechnique 12AU7 for the output buffer. This to get both lush midrange and better top end and base. I would appreciate hearing from anyone who has done something like this. Thanks for your help. Dave