Dear Kenjit,
This is my first post and enjoy going through all the different posts and often smile a lot. You need to take a step back, compare and try to understand the technical and acoustic differences between your two setups; the earbuds and the loudspeakers.
Like other mentioned, you are more sensitive to “timing”, which most loudspeaker out there have coherence problems. Even the “coherent” design, to a lesser extent. Multiple driver integration is done at a certain distance from the loudspeaker front baffle (more exactly the voice coil alignment) to the listener. A good listening room setup will place you exactly in the sweet spot, not much right or left, nor front or back. A single driver, a coaxial driver, the magnetic and electrostatic planar design will get you closer to your preference. You need to look at your listening position, and where these speakers are getting integrated, the “sweet spot”.
Also true, the room, its dimensions (room mode), its characteristics (liveliness to over damped), and how your loudspeaker’s placement (golden ratio…) is very important. The dipole loudspeaker with their figure eight radiation pattern could fair better in some rooms that the traditional “box” type.
Also true, your loudspeaker match to the power amplifier, tube amplifiers have response problem with loudspeakers with complex crossover network, and large impedance variations, specially the lower impedance. Solid state with design will have to deal with loudspeaker back EMF, screwing the sound with a poor feedback design. You need a good match between your loudspeaker and your amplifier.
So, loudspeaker coherency, their integration into the listening room, the seating and amplification are all components in your listening experience, and not in your listening path when you use the earbuds. There are some crazy good and expensive ones out there, but I don’t like that sound, I prefer the soundstage created in a proper listening setup.
I have not found an electronic/DSP solution to poor loudspeaker integration. The “monitor” loudspeaker allows you to move much closer to them, and they are designed to integrate much closer to the sound engineer. But they also rely on loudspeaker like the B&W to judge for the sound, and believe me, these are at the right location.
So, my proposition is to set back from where you are until you understand better what is happening. You are beyond experimenting, you need to benchmark where you are. And thrust what you hear, and your taste.