@skeptikal - There has been a lot of good suggestions and info supplied already. I I looked at the pictures you took of the room as well. Looks good, nice acoustic treatments as well. (Although the two small sofas directly in front of the speakers are probably not helping things.) After being in this hobby for 40+ years, the best suggestion I can make to you right now is to borrow a decent stereo power amp (for the front L/R speakers) and set of decent interconnect cables and give it a try. While upgrading to a better preamp, streamer, etc. should (and I stress should) be an approvement over the AVR, don't worry about them yet. Start with the 2 channel amp. You might like it, you might not. Either way, it may give you a better idea of what direction to go.
In the end, it is all about what you like and makes you happy.
... my 2 cents...
Jeff