But I could never get the powerful bass to work well in my room & eventually replaced them with something more manageably sized.
LOL a lot of people never got the hang of "PUTTY PINCHING"
It was pretty simple, really. You add mass to the passive radiator (after you get the placement right for the mids and highs) until you get "BOOM" in the room. If you already have "BOOM" in the room, then you remove mass (or putty) a thumbnail at a time, until it goes away. So you need to pick a passage of music that causes the issue and play it over and over. As time goes on, and the passive radiator wears, the boom will come back; a simple thumbnail or two every two years or so will fix it.
The trick was the compliance with his PRs, they were VERY sensitive. Modern PRs are a lot different; it takes up to an ounce of putty now to get the same results. I still add and remove putty on all my PR built subs. The last ounce or two is added to add boom and then removed until the boom goes away (per room, cabling, and amp). The difference is that it takes a lot more putty now with HE, high SPL (PRs) bass systems. Now, most people would rather use DSP vs mechanical tuning. I prefer to use mechanical first and then fine-tune the upper bass regions with PEQ/GEQ for dips and Helmholtz adjustable resonators for the peaks.
So your room probably got boomy after Brian tuned his speakers to your room (they loosened up), all you had to do was pinch a little putty, so to speak. Every room is different, along with the amp and cable combination used.
It was also the reason he added L-Pads for the mids and highs; every room and wall treatment is different. His tweeter and mid systems were HOT for a reason. They were for untreated and treated rooms alike. He was WAY ahead of the speaker game compared to some of his competitors. GR was one of his biggest critics, but then Danny didn't seem to understand that every pair of speakers was SPL matched to each other within .5% on the mids and highs for a reason. Every XO in every speaker was tuned to that pair of drivers and XO components. They were all SPL matched.
Heck, there is 5% SPL difference on most 20-50K speakers today. They all depend on DSP to fix all the mismatched driver and passive XO components.
I'll stick with my old speakers and speaker build concepts; they work very well for me. BUT I do like GR's servo sub systems, especially for playing records.

The rest of his speaker kits, not so much.
BTW, I still have a pair of Tower II SE (Rs). Serious BASS for sure.
Regards