I also wanted to avoid mounting and un-mounting them since it would be a hassle moving them to try other locations. I just threw together a couple temporary stands out of plywood and 2x4s for less than $20 U.S. You could even make the stands to simulate the joists and use the axiom brackets to mount them to the stand. Then just run some temporary wires across the room wile you test some locations.
I know if I was in your shoes I’d want to just get it done and start enjoying and showing off your setup. With any of the placement options you are considering they will sound great. However, for only a few bucks and a day or two you might get some peace of mind if the extra effort is worth it, or if you just like to tinker and can get away with it.
