Lighten the paint color on the walls and add lighter colored long sofa. Keep the chairs together on one side of the room. Replace the area rug with something that's not so busy.

Paint is by far the easiest way to update the room and make it brighter. Perhaps picking up one of the lighter colors of the rug.

Paint the walls, then post new photos and we can help arrange furniture and de-clutter. I would look at paint in the beige/tan family.

Palmeron, if you can transfer shots of all walls, it will be of help.

I agree that removing the cabinet will open things up for you. What is it that bothers you about the mantel?

How many people do you need to seat in this room? Which pieces must stay, and which must go?

I see you moved the leather chair. I was gonna suggest you switch the fabric and leather chairs and add a teal pillow and small table next to the chair in the kitchen.

Throw pillow: http://www.crateandbarrel.com/brenner-teal-blue-20-pillow/f64558

I agree to remove the large entertainment center for a console type or vintage buffet. I think your FP mantel works beautifully with all of your woodwork.

I would try a few things before you remove the entertainment unit. There are a lot of small items on the fireplace and bookshelves. If you have matching containers, use them on the bookshelves to contain small accessories - candles, frames, etc. I would also put the hurricane/candle that's on the floor in front of the TV in one of the baskets or on the top shelf. I would do the same in the kitchen with the items above the stove and cabinets. See how you feel. Simplifying the decor may give you the lighter feeling that you crave (don't we all). Then you can decide what, if anything, to bring back and what to put on your shopping list. The rug in the pic below is just a pet friendly one that I was trying...

I would arrange your new furniture like the pic below but flipped so the end table between the two sofas is directly opposite the fireplace. Maybe you could move the duncan phyfe table from your dining room to the window right of the fireplace or behind one of the sofas. This would definitely make the dining room feel lighter and give you the option of adding chairs at the ends of the table when needed. Lastly, I would move the wolf picture to another wall (see below). Leave the wall between the windows empty.

I should add that the ottoman, leather chair, and end table are meant to be your existing pieces. I just couldn't find good pics to use.