Woofers for SB acustics Sartori sb29

Would the ScanSpeak 18wu work?

I know that the Purifi work, as I heard their 6.5" under an SB and it was nice. But it had a pair of Purifi passive radiators on the back of the box.
The bass was much higher SPL than I was expecting.

Why not check out the kits at Madisound?

One very good and often overlooked option, besides Sartori and ScanSpeak are the FaitalPro line.  Great top end response + high power handling.