Can you not mount the sides on the wall with the included T bracket? That's how I would/have go/gone.

I don't drive my M80s very hard (peak probably 80dB at most, usually more like 60-70), but they work quite nicely with an old H/K AVR525 (75 wpc! woo!) in a 19x18x8 room open to the kitchen.

I am the Doctor, and THIS... is my SPOON!