The S4 uses the same size and fitting grill as the Rs4 and S-line A4's .
Non s-line bumper and the DTM have a shallow grille which wont fit the s-line bumper found on A4's with the s-line kit and s4 has the s-line bumper as standard , rs4 has a specific bumper but uses the same size format as s4/a4 s-line versions.
So you will need either a genuine RS4 grill or another s4 grille , S4 grill has dual vertical bars whereas s-line just has single vertical bars.
Rs4 is mesh.
You will really struggle to find anything suitable in an aftermarket format for the s-line size grilles, and the few that are around are rubbish.
best going with a used or new Rs4 mesh grille but be prepared to pay serious prices for either.