I'm using Klipsch La Scala IIs and in my opinion they're a great match with the 509X.
The LS IIs already have pretty stunning dynamics and smooth mids, as well as solid control of the bottom end. The L-509X complements all of those characteristics with passages that seem to literally move with dynamic expression.
Big, spacious, expressive sound... I think you have to hear it for yourself, I wouldn't know what you're benchmarking it against, but for me the La Scala IIs are a pretty great fit for the 509X.
Here's a video I took of the "1812 Overture" with the 509X and La Scala IIs:
https://youtu.be/sB_wChJ0RlI
The LS IIs already have pretty stunning dynamics and smooth mids, as well as solid control of the bottom end. The L-509X complements all of those characteristics with passages that seem to literally move with dynamic expression.
Big, spacious, expressive sound... I think you have to hear it for yourself, I wouldn't know what you're benchmarking it against, but for me the La Scala IIs are a pretty great fit for the 509X.
Here's a video I took of the "1812 Overture" with the 509X and La Scala IIs:
https://youtu.be/sB_wChJ0RlI