Interesting, would love to see a video of how does it sounds now.. If you left GPF and original exhaust on, I am wondering how much louder can it be.. I went for full Milltek turboback and it's a huge difference in sound. You are right, Milltek are currently the only ones that officially provide exhaust for GPF cars.. But I've been talking to some guys online and they managed to fit DAZA exhaust without much trouble, just always need to map out the sensors. But the whole thing should be from DAZA then, including downpipe.
As for mine, I've done about 300 miles now on the tune. First dyno showed 584hp and 698nm, but we know the power calculation was wrong (should be in 530-550 range), because of the brake on the dyno. So we're getting it dynoed again tomorrrow, will let you know.