Okay my friend! AND HERE WE GO! lol
Point 1: why oh why can't the TV be moved in front of that window and your front towers and center done from there? Why oh LORD why? Lol. Because all the things you want to do could be done from there. Just move the office stuff since its a corner desk to the back of the room couch goes in the middle. With that setup you could do not just 5.1.4 but 7.1.4 even 7.2.4!!! The room layout works perfectly like that
Point 2 go with the Denon 4400 I have it its awesome just always on sale cheap. Just perfect with all the features you need great reciever
Point 3 the reason Shady is suggesting against atmos where you currently are is due to spacing and dispersion issues. The atmos speakers in front and behind will be too close to you both front and back and your surrounds will be pretty close to your couch from that spot. Not enough room to make it work very well. However! Lol If we change the layout of furniture it works just fine.
Point 4 great speakers and subs have been covered but for speakers especially if you keep the layout the way it is and your speakers are fairly close around you? What about RSL's CG3 lineup? Super great quality you'll save a ton off money which will allow to invest in not just one badass sub but 2! Which every home theater setup should go with in my opinion at least duals
Point 5 I'm also thinking SVS but not just 4 subs. Although the PB 2000 and or PC 2000 subs in duals would be great in that room. But there ultra lineup. Not the towers if you keep the room the way it is but rather the Ultra bookshelves and ultra center! Save a lot and you get great quality at that price. Those ultra bookshelves have a lot of good reviews.
Now if you switch the room around and give yourself more room to breath bookshelves will still work but you could also do towers! Which means we can help you look at some options the SVS ultra lineup gets pricey there but as mentioned there's a lot of other great affordable options!
This should be fun but for the love of everything please do not go with those EARTHQUACK speakers! And installer. Run away run very far away! Just trust us on this one Lol