Some quick comments after speed-reading through the most recent posts:
1. I don't see the need to 'upgrade' your receiver.
2. Given that, your next upgrade should be center channel and/or subwoofer (assuming the Monitor Audio speakers work ok for you, which they probably will). Center channel doesn't have to match L/R but ideally it should (but then, even the so-called 'matching' center channel isn't a true match, as the only true match is a third tower of the exact same model, and that's usually impractical).
3. Whether or not to use the bungs can get complicated, as it depends on your tastes, your room, the speaker placement, Audyssey correction, etc. They're all intertwined variables.
4. The L/R speakers just need to be a few inches from the wall behind them (assuming they have a rear port). If they don't have a rear port, they can go right up against the wall. However, with one being close to a corner and one not, you might want to pull them forward a foot or two. Just experiment and see what you like best. Try close to the wall with no bungs installed, close to the wall with bungs installed, a couple feet from the wall with no bungs installed, etc.
5. When you find a positioning you like, then re-run Audyssey.
Side note: That big glass table in front of your listening position is bad for acoustics, as you will get direct sound from the speakers plus lots of reflections of sound off of the table. If you can't or don't want to move it, consider putting some books or magazine or pillows on top of it to break up reflections.