I'm temporarily using a PrimaLuna Dialogue preamp with my TRP. I've found going for the sound I like for each independently has worked well so far, along with adjusting other parts of the system. I've got early 1970's NOS KT-66's in the TRP and am now burning in a Psvane WE274B replica rectifier to compare with an RK version, which is very good. With the PL, it came with well-used Mullards, which I found too cool, so I replaced them with Brimar CV4003s, four of the six being the better 13d5 version (12Au7 equivalent). I should say that with the TRP I've tried a number of tubes before settling on what I mentioned. I did try some older Mullard EL34s recently in my TRP, but they didn't have the clarity of the KT66's. I don't know if the latter would work in your PL, but they are great tubes if you can find some NOS or barely used ones at a decent price (typically from England, either direct or via eBay, which takes care). Feel free to PM me, if you want to dig deeper on this.
