Whatever it's putting on the road from a performance stand-point, it's not because of a weight advantage. They're heavy cars, at least 400 pounds heavier than an SRT6.

This is the spec on a 2001 S4 twin turbo.

Length: 176.7 in. Width: 68.2 in.
Height: 54.9 in. Wheel Base: 103 in.
Ground Clearance: 3.5 in. Curb Weight: 3704 lbs.

They've only gotten heavier since. The next generation V8 S4 that replaced it is well above 4,000 lbs. The new supercharged V6 doesn't lose much of that weight.

But...manual transmission/AWD but it doesn't take much in the way of mods to turn up the boost. Like our AMG built 3.2l, the Audi's engine can handle a lot more.