All the larger speakers use T-Nuts but the smaller ones like the one Pi and two Pi use wood screws. The holes are drilled first, so the installation is clean. It wouldn't be much extra trouble to substitute T-Nuts for wood screws, but you won't need them unless you think you'll be opening them up a lot.

We don't make grilles. If grilles are desired, I suggest using velcro strips and generic grille foam. We did make grilles at one time. The first cabinetmaker I worked with - who still lives here in Tulsa, by the way - made frames and stretched wicker over them. The frame was then attached with velcro, similarly to the foam I've suggested. The framed wicker grille wasn't very heavy, so velcro mounting worked very well. I can ask him if he would be interested in building you a pair.