Congrats!
I was gonna mention how Best Buy is clearing out the AVR-xx12 models right now. Glad you found that deal
I know people tend to think of acoustic treatments as a "tweak", or they leave them as the last thing to do on their list. I understand that thought process, since acoustic treatments are not common, and people really aren't familiar with the benefits.
I have to say though, in your case especially, you should really try to address that wall right behind your main couch. In your diagram (big help by the way

), that couch looks like it's pushed quite close to the wall behind it, plus it's in a bit of an alcove with that short wall right beside it as well.
A great deal of your clarity and dialogue intelligibility problems are coming from that. And changing your speakers isn't going to solve the issue. It might sound different with new speakers, but the cause of the problem is still the seating placement.
Step one would be to pull the couch as far forward as you can. But I understand that the layout of the room won't allow a lot of space between the back of the couch and the wall.
What will really help you though would be to put some nice, thick - as in 6" panels - right behind your couch. Maybe get a good bass trap in that very close corner with the short wall as well.
You say you've not decorated the walls yet. Take this as an opportunity to go over to Acoustimac and get some printed bass trap (6" thick) panels for that back wall. 3 panels spanning pretty much the whole wall would be ideal. But even just one panel right behind your primary seat would be a big help. You'd notice a big difference in the clarity if dialogue with this change.