I have a pair of type07’s and 20’s. Due to changing life circumstances and personal wants, I’m considering selling stuff and getting 30’s. My friend had them, and while they sounded great, he was in a fully treated studio. I have 6" thick Corning panels but they are not currently in use (moved to a smaller apt).
Bottom line…I’ve read that the 30’s can hit higher SPL but not much else. It’s a second woofer, that’s it, I believe. The 20’s versus the 07’s is a huge change in drivers and enclosures.
I’d have to see a substantial gain to make this worthwhile. I love using my 07’s at my desk and my 20’s in my living room. It’s the best setup I’ve ever had, and makes my old B&W’s a joke, sadly. But I don’t want to go through the cost and headache to replace everything for a marginal SPL gain.
All other things being equal, the second woofer will lower distortion in the frequency range where every speaker has the highest distortion–the bass.
Now, if you like the 20s and find their low end balanced and still to your liking when the volume goes up, it’s probably not worth it.
Sorry can’t help you, just wanted to say that I have the Hedd t07 with a SVS SB2000 and it’s the dream - when seated in front of them. Their off axis response isn’t great to my ears, but that’s not an important factor to most.