Hi gwbailey,
How's bedford falls these days?
I'll try to answer your questions as best I can..
When I built the false wall, I use 2x1 wood, and made sure the studs were at 600mm centres so that the edge of the boards line up with a stud. Then just cut the slabs to fit, and fill any gaps with silicon rubber (high modulus is best).
Another way to fix these to a wall is actually on the pack - use tile adhesive to fix the slabs to the brick or breaze wall, then when you put the plasterboard up, you drill through the board and slabs and into the wall. Use rawl plugs in the wall, then long screws to screw the plasterboard into the wall, sandwiching the insulation between board and wall.
Really I think you should build a false wall with a gap behind for extra soundproofing (4x2s are ideal, with an inch gap between that and the wall and fit 4ins of insulation). This makes it easier to screw the plasterboard to as well.
To fit two layers of plasterboard, you fit the first layer using screws into the beams, then do the same thing with the second layer using longer screws. Before I fitted the second layer, I sealed the joins between each adjacent board with silicon rubber. I also used some liquid nails between the two layers to give some extra rigidity. Then use self adhesive scrim tape (it's easier if you don't do a lot of plastering yourself) and plaster across the joins. If you use a good straight edge you can get a good finish with tapered edge plasterboard.
I did not leave a gap between the slabs and plasterboard, as I'd already left a gap behind the false wall.
I'm not attaching the speakers to the walls because I don't want to transmit any sound/vibrations through the wall if I can help it. I'm using stands. But if you want to hang things on the wal, you can get special plasterboard rawlplugs. What I tend to do is drill a hole, use some no more nails in the hole and fit a rawl plug. I let it set before screwing into it. This seems to stop the plug turning or pulling out.
The best way to soundproof a ceiling is to build two false walls using 4x2 first, the put a new 'roof/ceiling on that, so it isn't touching the ceiling above. This is the most expensive way of course, and probabaly not practical.
Another way is to get some (expensive I think) insulating/soundproofing mat for upstairs. I have seen this used, and it included removing the skirtingboard. I think they removed the skirting to seal the gap between the wall and floor, and maybe even sealed the gaps between the floorboards. They fitted the soundproof matting right up to the wall and sealed any gaps, then refitted the skirting and sealed al gaps between skirting and wall and matt. Then they used high quality underlay before fitting the carpet, though I don't know how they fitted the gripper rod to the matt/floor.
If you can get all floor boards up, then fill all the joists with loft insulation, then refit the floorboards and seal all gaps with silicon. Fill any gaps between skirting and floor with silicon, then use high quality underlay before fitting the carpet. Fit another layer of plasterboard to the ceiling in the ht room.
Those are probably the cheapest options. feel free to ask me any more questions if there's anything else I can help you with.
Gary.
Now use the high quality underlay