Has anyone had experience with the products from "ligno"?
Not personally. Only from my customers. It works well, is insanely expensive - but a normally furnished living room serves the purpose at a fraction of the price and with clever use of sound absorbers on the wall (decor or as a picture) the living room works better than ligno.
The lignownad simply won't do anything for the bass range. It can only help with the highs and a little with the mids. However, these are anyway low in energy. Just google Helmholtz resonator, that would be, in my opinion, the method of choice.
Nevertheless, I would prefer to address the problem instead of solving it with software.
But that would be the first step, to tune the sound system to the room using the onboard features. Structural measures are therefore not off the table. However, hard walls and many window surfaces do affect the room's acoustics.