Just wanted to pass on a bit of info, which may not help those who are not in or near the Bay Area, California. A local, but well know, tuner (www.factorypro.com) has a device similar to the PCIII. It piggy-backs on the stock ECU, and the techs at Factory Pro can custom map (they use a dyno) for your bike. It's not manually "tweakable" by the owner after the install/tune, but these guys stand behind their product and have told me that any re-mapping needed down the line is "free" (can't vouch for that myself yet).
I've had these guys do my '04 ZX-10R and '03 Tuono in the past and the results were top notch. They quoted me at $775 for the part install and tuning OTD. I'm going to have them dial my bike in after I install the Arrow full system and (maybe) modify the air box.
Please keep us posted on how things work out. I’m waiting patiently for power commander to come out with something for the s4rs. Chris at desmoworld said he had success with modifying the connections on a pcIII to fit the RS
I can't see how the Ex box will require a whole lot of ECM tweak. It can't be much different than just running the collector without the stock slip ons. They're about the same size (cu. volume) and should have near the same amount of internal baffling. The Ex box may have a little more baffling which probably brings it inline with the stock slip ons. I think I saw a power curve/torque mapping for the Ex Box that showed a shift in the curve but not by a whole lot. Even with a cut airbox and hi flow air filter your S4RS will run fine with a minor touch up on the air/fuel mixture without swapping the ECM. At least mine does, but I had the shop do mine for me.