Ok an update ...

I decided to put in some wood strips (3/8th strips ripped from 2x4s) to hold the MLV away from the channel. (see 1st pict). When I vibrated the channel you could hear it whack'en the MLV in places. Once again a questionable need for a sound you'd probably never hear ... yet another one of those safe then sorry decisions ... yet another delay ...

But the first layer of wall board is now mostly all up smile
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In the middle of the room the last full sheet (of this layer) is being prepped. On top you can see a bunch of cut OSB pieces with matching floor muffer. These are being screwed to the back of this board so there is some wood backing to hold speakers, attach molding, or put in electrical/speaker boxes.

Screen wall:
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