As far as the NEC is concerned, you don't have to run low voltage wiring to a j-box.
I would suggest installing low voltage trim rings, instead. (not to be confused with a mud ring)
Also, work with the guys doing the sheetrock install. Since you know exactly where you want your speaker wire drops, and trim rings (for volume controls)to go.
If you're there, wires won't be buried, and you can assist in poking the wires through, right where you want them.
Good Luck with your project!