Yes, I put insulation up first and pressed the backer boxes up into the cavity. They are pretty much spring loaded in there and I had to put the screws in on an angle to suck them up higher.

I was thinking as I was doing it the pros and cons of keeping them that way. Looks like even though the speaker will never be in physical contact with the box the sound will cause vibration through the box--->insulation--->floor. I will have to revisit these and remove the insulation.

So I should put nothing behind/beside the boxes in the gap? I wish I made the boxes shallower, but that really limits speaker choices.

When it comes to soundproofing Seems like:
More is not more.
Less is not more.
Just right is more.

Thanks Nick! That would've sucked big time.