As you probably know, all of the Termis for the S4R are not yet available from Ducati. And they don't when they will be. Sometime this year, maybe.
As far as I know, Silmotor makes a system for them. Check with Spareshack. Spareshack also has a header system that eliminates the cat, but this doesn't with at all. We've tried it. Obviously, they hadn't!
The only other option to consider (and we did as well) is to use the header pipes from a 996R or similar, a real 57 mm race system and then use a good fabricator to finish the rest of the system. But, these header pipes are very expensive and then you still need to do a lost of work to get a full system.
To be honest, I think the Arrow system is very well suited and has room left for engine tuning. And with the removable baffles taken out, it sounds VERY nice.