Installation Guide for bTres X1 in an RS3
Make sure your car is turned off. You do not need to unplug your battery.
Installation Steps
Step 1:
Open your driver side door and remove the trim using the trim removal tool that was provided in your package. It will pop right off very easily.
Step 2:
Remove the bolt pictured here so that you can remove the panel below the steering wheel.
Step 3:
Remove the two bolts on the underside holding the panel below your steering wheel. Then pull the panel off. There are a couple tabs on either side of the steering wheel that will really hold on to it. The couple cars I've done I had to really yank it off, nothing broke, but be careful once it comes undone to disconnect the headlights switch otherwise you run the risk of breaking that wire. Once you have this panel removed set it aside.
Step 4:
Remove the driver side fan vent on the dash with a trim removal tool by gently pulling/working it out. 
Step 5:
You'll need to drill a hole in the vent duct and feed the USB C end of the cable from inside up into the vent duct and out the top. The base of the bTres X1 now comes all put together (this image shows the base removed). You shouldn't have to remove it. Once you push have the USB C ran up there, you can push it through the pre notched blades in the X1's vent cover and then plug it into the bottom of the X1.
You should fill in the hole you drilled with some silicone to keep the wire snug and air flowing through your duct as it's supposed to.
Step 6:
You are now ready to simply push the X1's fan vent cover into place
Step 7:
Run the other end of the power cord (red) as shown to the fuse panel. You'll remove the specifically pictured fuse, which is a switched fuse, place the fuse you just removed into the empty fuse slot on the provided splitter. Now plug the fuse splitter into the fuse slot you just pulled the fuse from. This is the only fuse I'm aware of here that is a switched fuse. So make sure to use this one. Then find a place to attach the black ground wire to. Suitable places are usually any metal bolt that is connected to a metal frame of sorts.
Step 8:
Test, when you turn on your car ignition, your bTres should come on after 30-60 seconds. If it comes on, you are likely done and ready to put everything back and enjoy. You may have some codes that you'll need to reset using bTres or ds1 web interface afterwards.