Had my Primaluna Dialogue Premium Preamp about 18 months.
My setup is a modified Oppo 103, Coda Amp and Thiel CS5's.
1. I got out of the stock tubes pretty quickly and have not reinserted them.
2. I could not tell a difference with different rectifier tubes
3. I have changed all six au7 tubes but the middle two are we you can hear a difference. Using Mullards for the outer two pairs and switch between RCA's, Telefunken, Seimens, Brimars, GE's, etc. for the inner pair. In my system, I seem to like the Telfunkens because they provide a better texture to the mid range and bass.
4. Have kept the standard power cord.
Dsper