Well ive found quite a few pics of the S4 engine, but its impossible to see what type of s/c its using (which was the main thing i wanted to know) and how they have piped it, as its buried away under everything else...

I "THINK" by following the piping, that the turbo is first, then it goes thru an intercooler, then it blows thru the supercharger, then thru the second intercooler, then into the inlet.

VERY strange way the dumpvalve seems to vent tho, but im sure its the DV (my first thoughts were that it was the superchargers "wastegate" so to speak, and the boost pipes are done a different way to how i mention above, but its too close to the throttle to be that...)

(Id post the pics but it wont let me right click on em, and actually its well clever, they not even Jpeg images, theyve cleverly made them like desktop backgrounds so you cant rip the pics off....)