You can get armchairs that swivel. But you need pics for more advice than that.

We need a drawing of the room and measurements too. This is not enough information. First thought is to make a small seating area at the end of the room near the French doors. Then configure everything else around the TV needs. You do not have to have one focal point in a large room. Break the room into different areas and each area can have a focal point.

I guess there's no other room for the TV and audio equipment to go in? Hard to give you any advice without photos and measurements.

Well I think we can only guess with no pics or a to scale plan. If the audiophile drives the bus then he has to get into the mix and expalinn what he needs . My hubby is one too that is why we do not have TV in out LR so we can enjoy music with proper speakers .

Only one wall is angled - the one you've chosen as the TV wall. The other one, with the interior door, is straight.

What are the green marks on the floor plan?

What do you think about another chair in the vacant corner by the french doors? This is where the best terrace views are. But as the french doors open inward, everything at that end of the room would need to move further back into the room by at least 30" to allow the doors to open. We are considering replacing them with sliders to mitigate the lost space at that end of the room.

And perhaps placing the TV on the straight wall makes more sense than the angled one? What do you think?

Also, is there any way to make the dated built-ins on the fireplace wall look more upbeat? Or should we get rid of the whole lot and start over?

Love your ready ideas and speedy feedback. Thank you so much!

Here is the revised plan with the one wall straight and the other wall at an angle.

The rug is 9x12

I'd recommend you purchase or have made a floating piece of casework mounted to the wall to be placed under the 75" TV

The green lines indicate wall areas that would benefit from art or wall decor.

Depending on the size of the chairs you can place them in many places. I only placed a large chair/recliner on an angle at the terrace door because many people seem to like the option of a recliner in a space to watch TV. I only placed one because I didn't want to impede access to the opening or visually block the view.

Your other option is to use a sectional instead of a sofa and chairs.

You're in the land of leather...........I hope you find some great seating for this lovely room.

Since you rarely use the fireplace I left the dining area in that space. You can use the built-in partly as a bookcase and partly for dining area decor.

By the front french doors, I show 2 swivel armchairs that can be turned around to be part of the conversation area.

Note: For the floor plan, I have used the dimensions you show but not sure about the angle by the front of the french doors so the room is 13' wide top to bottom with the 3' added only by the entrance doors.