Nice car and spec you found there.
The Audio gear
It's going to sound really good. Just get someone with VCDS if you don't already own it. to change the low level output on the radio and linear as well.
You also need to be aware, you can't fully disable the setting in the radio that adjust the volume speed and road noise dependent.
I'm going to enjoy seeing the photo's of the stereo gear fitted thats for sure.
I would recommend removing the GFB DV, it's a gimmick is the best way I'm able to explain it. We did some data logging on an S3 and it was all over the show.
At only a few RPM bands was the requested and actual boost the same. Mainly as the GFB is very slow at operating.
we removed the spring from the GFB and it operating quicker but still not correctly.
replaced diverter with a Rev G and the car is much more enjoyable to drive, thats for certain. Much quicker as well.