Got the 9s since I already have the LYD-7s from Dynaudio - they say the 9s was created especially for the LYD series of speakers so it was an easy choice for me.
And a good one, too! The sub is tight, punchy and rather detailed as most sealed designs are.
Build quality is good and just what you'd expect from a sub at this price point. Don't be fooled by the 9.5" woofer, it plays well in small rooms(up to medium ones) I did prepare a bit before getting it: some bass traps in the front corners and installed REW plus measurement mic. After unpacking I spent a bit of time with the placement and measurements to get it the sweet spot and phase and time aligned with the main speakers, it was a bit of work, but you do it once every now and again, so it's fine.
It's weird to review a sub by itself as it's supposed to part of a bigger system. Now that I've integrated it properly with my lyd7s I think it's better to talk about the system as a whole now that the 9s was added:
The bass goes lower(no surprise there). Soundstage is now deeper(taller to be precise) more natural. Low mids are now cleaner/less muddy. Mids and low mids have better transient response, are less compressed, more detailed. Everything is just better across the freq range. The lower bass extension is only half the story, the other half is the speakers being released from bass duties and really shining on the rest of the range.
The difference is not subtle, either. I really feel that I made an upgrade.
Now, you may want to take all of this with a grain of salt, as speakers with high crossover frequencies like the LYD7s, Neumann KH 120 II or Barefoots which are all at around 4khz, do benefit way more from unloading the bass duties to a subwoofer then most speakers, that usually have the crossover at about 1.7 to 2.2khz.(but the later also benefit, don't be worried)
Conclusion: The sub is good, just what I expected, it's the only sealed solution in that price range which makes it a no brainer even if you don't have the matching speakers or high crossover ones.
I highly recommend!
Cheers!