Dual Playbase

Splitting SPDIF is not a big deal. Splitting HDMI-ARC is a problem, however you could use the HDMI-ARC optical adapter, then split its SPDIF. This would work fine for you since you are not attempting ATMOS. Likewise, you could split a TV’s SPDIF output and use multiple SPDIF to HDMI-ARC adapters for multiple soundbars.

Subwoofer and listener placement in the room are critical for aggressive bass. Adding more subwoofers, all at unfortunate locations, may not accomplish much. That said, the critical locations are sharply defined and there are a limited number in the room. If you are using multiple subwoofers, maybe some of them will not be at the unfortunate locations.

Let’s explore the physics of your rooms. You’ll need a handful of Post-it’s and a magic marker.

Play a thumping bass track and walk the room, close to the walls. As you walk you’ll notice locations where the thump is accentuated. Mark these locations with a Post-it. You’ll also notice a few locations where the bass is doubly accented. Mark this Post-it with !!. When you step back to survey the room, you’ll notice that the Post-it’s are more or less symmetrically distributed around the room. These locations are known as “peaks”. About midway between two peaks is a “null” where bass will be minimal. For maximum bass you want to place subwoofers and listeners on !! peaks. As you become familiar with discovering peaks and nulls, you’ll be able to discover smaller peaks and nulls in three dimensions throughout your room.

These peaks and nulls are sharply defined. In my college apartment I discovered a monster peak and placed a chair at the peak. This was a favorite spot for male listeners because bass seemed to explode from inside your body. If I moved the chair a few inches the peak was gone.

#buzz

The Home Cinema-room is very hard to explain…i wish i could show you/someone by a pic or video. 
I have been trying a lot of stuff including all sort of Trueplay-tuning(mic close,mic far away from speakers/sub/soundbar) and no Trueplay-tuning.

Yes i have some spots in certain areas that have more bass than other places. Out of that observation i have placed the sub on both ends of my sofa,one close to a corner. The other sub do not have a corner and i think that one play out of fase and some volume lower than the one in the corner….i’m not 100%sure.

That’s enough for me: I’m out.