Oh my... I knew my audy-sense was tingling for a reason.
Lot to unpack. Most of our "mainly for music" systems don't go in the ceiling. In fact, the snobby audiophile in me died a little bit when I read that...
![Stick Out Tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
That AVR is the wrong unit for the job, and has been stated, wiring speakers in parallel to one channel is a pretty big no-no. I might even suggest you contact a pro installer and see what he could do for you.
You bought some nice subwoofers, which tells me you want good sound. Then you stick all your speakers up in the ceiling! As far as placement you just lined them up with the recessed lights? Is the goal just to have some background music or are you looking more for good sound and performance? I think in wall speakers would be a much better compromise between aesthetics and quality sound than sticking them in the ceiling.
Bookshelf speakers or monitors on stands acceptable? You can get into some really nice sound without breaking the bank right off the bat with the subs you have.
Or you could get an AVR with more output channels and use "All Channel" or "5 Channel" stereo. Then all of your speakers will get the same mono signal. You can't really do proper stereo or surround the way they are now anyway.