"+16db spikes at 32hz" Yeah, that's a problem! At least you know the KEF's can dig deep..I am guessing though that such an issue would be from a movie soundtrack rather than a musical track.
You may not really need the subwoofer especially if you don't listen to music that dips below 30hz. I had used a sub for a few years but realized it was overkill and listening without one put more emphasis on the midrange frequencies - which is where most of the music resides. Doesn't help that I am getting older and my hearing is fading.
Two ports on each speaker that houses 4- 6 1/2" woofers is fairly unique, especially a port that high up on the speaker. Throw windows and a sub into the mix and I see your dilemma and a need for measurements/data. To add to that scenario, the Brimar tubes are likely to add more bass. Good luck with that! ;)
As for the Rogue, I typically turn it on a couple of hours before I listen. My understanding is that a preamp with tubes can be left on at all times, but not the case with an amplifier. My DAC is on all the time, as Schiit suggests to do so as it will better the results.
Please be sure to share your thoughts on the tonal changes of the Brimar tubes once you have had some time with them as they are on my want list.