Phew.. long time no update.
Been working hard on the rest of the basement, not much say about the theatre room.
Threw in a few "Tapcons" to hold the subfloor down (1" XPS and 5/8" T&G Plywood) because in some areas where I used PL400 glue they had lifted, either because I didn't put enough heavy stuff on top, or because I didn't put enough heavy stuff on top.
I quoted "Tapcons" because I used identical concrete screws by Paulin sold at Homme Despot Canadaland, sized 3/16 x 2 3/4". They specify to use 5/32 bits, but I found I was stripping them far too often. What I did instead was use 3/16 bits on a rotary Bosch hammer drill (again rented from HD Canadaland). Tried initially using my cordless hammer drill (the green Hitachi in the picture) and a borrowed Bosch corded hammer drill. Both were a waste of time.. the rental cut through concrete like a hot knife through butter.
Anyways.. first I used a 1" spade bit to create an indentation at a depth of about 1/3" so the tapcon head wouldn't poke through. Then drilled a hole about 3.5" deep and vacuumed the dust out. stuck in a length of 16ga wire cut slightly shorter than the screw, then followed that with the screw with a 3/16 washer to give more holding area for the screw. Used a drill to thread it in, then tightened it by hand so as not to strip it even more. Darn things are super fragile.
Here's a closeup:
And the rest of the room:
Carpet's going in tomorrow.. so excited!