Sorry to dig but I see that you have a cut-out hole below the wall/cabinet that looks like it was originally planned for a subwoofer.
What happened in the end? I'm currently planning to do the same for my yet-to-be-built feature wall (subwoofer in cabinet).
Also I see that there's a room behind the tv wall. How's the sound travel into the room behind?
The cut out cabinet you see that's below the left speakers is for my receiver. I posted a picture of it in the same post. The cut outs are for ventilation, and for the remote control IR to be able to reach the receiver. The sub is actually to the right of the sofa (also pictured) and it's not enclosed. Actually, you can see another taller cabinet on top of it, but without cut outs. That's for storage. Both cabinets eat into the built-in wardrobe space in the room. There's no issue with sound travelling into that room since usually we just play background music, or when it's movie night, the whole family is watching and nobody is in that room.
I don't think it's advisable for subwoofers, or any speakers, to be placed in cabinets.