So I used XS power previously on my Audi that I had but had no idea that they made downpipes for the S63TU. They are incredibly cheap, I mean less than $300 for the pair. I bought these to try them out and honestly if they didn't fit it was only $300 instead of some $1500 set that may or may not have fitment issues. I feel like $300 is a good amount to take the risk, so I did.
in Short these are great, I totally recommend them. they have the best price for downpipes, I think the welds are pretty good, but I am no weld expert, and they fit pretty well. here is the link to amazon to buy yourself a set.
https://www.amazon.com/Dual-Turbo-Do.../dp/B078PLXQ28
I think these operate just like any other set of downpipes for these cars just for far less cost. I was even able to use my OEM heat shield. I could not use the OE heat cups around the heat shield since the pipes have shorter O2 spouts, whatever not a big deal. I like having the heat shield on just in case, and no one knows the wiser other than the insane sound these things make. I mean really these pipes make the car sound evil.
I had to adjust the brackets that hold the pipes in place to get them to fit well and that's it, I mean about 5 minutes of flexing the bracket and they sat perfectly, I followed the VRSF Downpipe DIY on these forums and it was butter smooth. These V-Bands on the downpipes even have the little insert lip into the turbo housing, I have seen a few sets without the lip and they don't seal as nicely, these have the lip and seal really well.
It drones a little @ 2k RPMs with my valves open on my FI Exhaust but with the valves closed its nice deep and throaty, with the valves open its just so loud, I might actually change from using my car always with valves open to sometimes running closed valves since it sounds good there too, and not like a Prius, finally!
In all I totally recommend these and their price point cant be beat.