Well, it's 3 months later and I haven't moved much ... the guy that's helping me needed to take some time and we have just started up again. Finally putting back up the channel

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In the mean time a few things changed. I've decided to use OSB only on the ceiling (to hang speakers) and on the electric wall (a 3' wide wall section which is inside a 11" alcove turned cabinet). Between the OSB and the wall board sandwich I'm putting some squishy floor underlay (thanks Trevor) which will hopefully allow the sandwich to vibrate a bit (who knows if it will work). The other walls will just be two layers 5/8s wallboard with green glue. I'm not 100% sure if I'm gaining or loosing by getting rid of the OSB behind the walls but at least I know what to expect performance wise.

I also doubled up most of the in-wall wiring that the electrician put in. It was too small a gauge for most of the runs and they did some creative wiring ... one 30' run had over 50' of wire in it (my guess is they ran it to the wrong place and then just kept going). I would have pulled some of it but most of it was unmovable being in the spray foam insulation. Anyway now all speaker run have a damping factor over 100 ...

Finally a fire alarm wire was snaked and attached to the halls fire alarm and all the MLV was hung ...