It is always best to make sure your source components are the best that fits your needs/budget (cd player, tuner and turntable/tape deck). The rest of your system, wires-pre and power amps...and speakers will only have what is feed them by the source components to work with. That said, if you are happy with your front end (source) components, I would suggest trying tubes in the pre-amp and seeing if you like that first.
Tube sound: Pre-amp vs. amp?
I'm just an audio neophyte, so bear with me on this question: If I want to achieve a "warmer", tube-like sound, do I have to upgrade BOTH the pre-amp and the amp to tubes? I currently have ss components (NAD) and would like to take the edge off the top, but keep the detail, especially in the mid-range.