I built a 8" Noveske upper. My only complaint is that it will not function with subsonic rounds unsuppressed, but they state as much on their website. I believe the AAC is supposed to cycle unsuppressed.
I'll let you guys know when my stamp comes back. I'm building my own, 10.3" barrel. I have some input with the barrel maker so I'll make sure the gas port is right to cycle unsuppressed.
Not that it matters, because the Form 4 for the AAC 762SD-N6 will be going in momentarily. Just waiting on the Form 3 to my FFL.
I don't think the SD-N6 are shipping yet. I sent in my preorder for one last month to the dealer who is supposed to get the first 150 off the assembly line.
ETA: Just found on silencertalk that AAC is trying for an end of March delivery on the civilian versions.