Sure, I can elaborate further, although
@Lurch summs it up nicely.
The Olympica II are equipped with a variant of bass reflex that they call "stealth reflex", which they claim is an improvement on traditional porting to eliminate possible boomines. Now, the speakers were never, in my room, boomy. But they could not really convey a tightness in bass in the manner of sealed loudspeakers.
I have the privilege of regularly enjoying a fellow fishie's phenomenal system consisting of closed box monitors and closed box subwoofers. While quite different in presentation than my Olympica's - that bass performance is something I have always aspired to.
The addition of Gaia II's has tightend the bass, and in a way, allowed some more energy to reach the listener directly, resulting in a firmer low end with less waste. Additionally, as it typically happens, this has further cleared up the midrange and resulted in a more wholesome presentation.
Now, they did not transform the speakers into closed box variants, of course, but I am now way less tempted to trade them in for a Neumann setup, even when playing "Dŵr Budr".
I am not sure how they do what they do, but to me, worth every penny.
P.S. If you have speakers with a plinth, you may get away with the pro-oriented "Iso-Puck" which are a less fancy version of the Gaia (well, the Orea), but way cheaper. But you need a flat surface as those have no threaded mounts. I have the "Iso-Puck Mini" under the Devialet, and under every component in my headphone system.