Upgrading power cables

For me, upgrading the amp PC first made a big improvement in the system as a whole.  Using a high currant cord I got much stronger bass, a wider soundstage and more detail across the board. 

Upgrading the source cords further refined the sound to varying degrees, but found good pairings after a bit of trial and error (I have a mix of Shunyata, Kimber Palladian and Clarus Crimson).

I just changed my CD player and tried the stock cord first (it is a pretty nice one as stock cables go), but an aftermarket cord was noticeably better, particularly in the bass, mids and vocals.

The power cord is the most important cord in your whole system.  Change all of them.  Its easy to make your own.....use top grade components. (oops...I found no difference in the power cord to my turntable...but other than that one....)

You usually match a power cord to particulat component so they don't have to or should not be the same or even the same brand. That said, if you want top of the line they might turn out to be the same, maybe.
It varies which component will be more sensitive to the upgrade, it is hard to advise. In your case I would probably first upgrade your tube preamp cord, then the source and the amp the last.

"Honey, looks like I'm going to need a power conditioner."

"OK, dear, whatever you need."

Ha!  It will be another whole thread to cover a power conditioner. 

At least your significant other is a real keeper :)