I think while in theory this should work - cutting these packages open with nothing to hold the cellulose in place will just result in it going everywhere. I have worked extensively with this insulating attics and you will have to make sure that you build something to contain it. You could face the wooden frame with polyester (similar to the stuff that's used on box springs) to hold the insulation in, but getting it packed densely enough into those spaces might prove difficult.
I would say you're better off getting Rockwool RHT40 or RHT60, or RockBoard 40/60 or Owens Corning 703/705. These are compressed insulations and have very good acoustic coefficients, even down into the upper bass frequencies. The main advantage with these is they are easy to cut and cover - they make excellent broadband absorbers and can be 'tuned' by establishing air gaps behind the material in conjunction with different densities and thickness.