Don't do it man, hate to burst any dreams but I'd hate to have you invest all your time and money. If you want it just for simplicity or to go a different direction then go for it, what is nice is the cleanliness of the system when supercharging a 2.8L, with no piping, dv's, n75's, boost controllers, etc, etc.
But when it comes to performance, power, there's no and I mean no comparison.
And comparison against what? A 100% stock 1.8T with the general goodies, a bolt in equal length tubular manifold and a small baby GT2871r Eliminator (baby version) destroys a supercharged 2.8L, there is zero and I mean zero comparison vs a 1.8T, not alone an S4. You'd only do it to be different, but don't expect to be powerful and forget those hp numbers not going to happen or even if you dumped ridiculous amounts of money the powerband will be so bland and linear and offer no punch, aside from the launch, but then just goes back to being a slug. The 2.8L V6 is literally thee worst VAG motor ever built, ever! Even a 2.0 8V is a much better motor (I've been talking performance wise, not reliability wise as there are no known bad apple VAG motors).
Just saving you the effort

, you'd do it just to be different, not for performance.
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