Audi started off their V6/V8 engines with plastic engine covers, and fairly rough valve covers. The valve covers didn't really need to be smooth, as they were effectively hidden by the plastic shrouds.
The C5 RS6 BCY engine is no exception, with the difference being the engine shrouds are carbon fibre, the larger section being the integral airbox.
It's interesting to see Audi have come back to exposed engines, with the valve covers being exposed. This has meant the valve covers themselves have become more attractive, smoother and easier to clean. The plastic engine shrouds first disappeared on the 3.0 V6 30V (ASN/BBJ) in the B6, and the 4.2 V8 40V (BFM) in the D3 A8.
With my last build, whereby I installed a V8 from a 2005 D3 A8 in my 2000 B5 A4 Quattro, I liked the clean, minimalist look of the motor. I was able to have the valve covers professionally painted in a shop, in the same color as my car.
With my current build, I am going with the same look. To this end, I have purchased the later 077-serie V8 (non-FSI) valve covers, with their matching timing belt covers. I have. Ordered the rear sections too. The timing belt covers will remain in their stock black, while the valve covers will be in the same color as the exterior of my car. Very similar in appearance to the valve covers of the B6 S4, but totally different in fitment. And, they are aluminium. I believe certain years of the B6 S4 valve covers were plastic, perhaps?
Pictures!