2 years ago Ron at New Record Day stated the Spatial M3 Sapphires with their passive bass woofs were "faster" than Danny’s servos......he compared them several times. He talks about this starting at 28 minutes in.
https://www.youtube.com/watch?v=iFQKGaxfIJk
The servo subs are great.....but they are not state of the art. The guy at GT Audio was using the servo subs and is now using Acoustic Elegance woofers in his H-frames.
The servo subs also cannot play that high and have limited tunability. Using a xover/amp you can set the xover anywhere you like with the AE woofs and equalize to your hearts content and get rid of all bass nodes.
Please read this review on the Kryon speaker using AE woofs.....the guy said it was the best bass he ever heard in his room. Of course, you need to make a serious baffle and brace it well. Kryon uses the AE woofs in all their open baffle designs including the monster one without any baffles.
https://6moons.com/audioreviews2/kyron/1.html
https://kyronaudio.com.au/gaia.html
Joe Cohen of the Lotus Group designed the two Granada speakers shown here (using the same AE woofs).....way over 12 years ago. You can search for reviews.....they were loved. Don’t know if any were sold.