Thanks for the tips. I thought about the plywood, but my ceiling is SUPER tight. It is only about an inch or two away from the studs and I have to bend the tiles to get them in and out. Plywood would be tough. I picked up two brackets to mess around with....
The first one would compress the tiles as you mentioned. But maybe you can leave the speakers a little loose? It's the t-bars that hold them up anyway.
The second one is interesting. I was thinking about removing the t-bar/bracket from the pot and screwing them directly to the side of the M3. This way I do not need the flanges on the speaker to secure it. Those t-bars also have a height adjustment screw, so I might be able to adjust the speaker so it's not compressing the tile.
I am going to call Axiom on Monday and see if I can order an in-ceiling M3 enclosure, without the speaker. This way I can experiment without spending the money on a speaker I may or may not be able to use.