I'm pretty sure it is, the two layers of OSB on the sips must cut down the noise a bit.
Foam is known for great sound transmission, I hoped 5.5" inches of it wouldn't be as bad..lol
When I spoke to the guys @ CCHRC, they said they put 1/3 of the total R value on the warm side of the REMOTE wall...in Alaska. I think damp sprayed cellulose will be easier to install (no need for insulweb which would be tricky to staple behind the posts/beams and the ability to spray it in all the tight nooks and crannies behind braces, post and beams). I also heard it can be left exposed as final finish. I think with a light layer of some natural covering to blend it with the studs and then painted, it would:
#1) provide a barrier of natural material between our living space and the Polyiso
#2) keep drywall out of most of the house
#3) blend in great with the funky theme of our house

The house is performing great. We've been breaking temp records in the last two weeks with temps dipping down to -40C at night. I am still able to work upstairs in a shirt. There is currently no heat being directed upstairs, the only heat getting up there is from the basement through the cracks in the subfloor...a redneck heated subfloor you might call it..lol The mainfloor still has a lot of undetailed section where we're loosing some of that heat too, so I have a feelin' our 4 cubic foot Hearthstone stove might be a lil' overkill once we're running it next winter...