You already own the Active Autowerke Signature Series X pipe for your BMW E9x M3 to achieve the maximum in performance and power, but were limited only to the race track since it replaces the BMW factory exhaust catalysts and was not intended for the highways.
The Active Autowerke Stubbies is designed primarily as a cost effective means of utilizing your existing BMW Factory catalysts into something useable. If this can be done, then there is no need to purchase as set of catalysts to be OBD11 readiness compliant.
The Active Autowerke Stubbies with your BMW catalysts will do the task of meeting OBDII readiness requirements when instaled with the Active Autowerke X-PIPE. Of course, the feature of the added performance is still maintained.
You will find that the front section of the Active Signature X pipe is totally removable by the use of V-Band clamps. Simply remove this front section and replace with the BMW primary catalysts that are converted with the Active Stubbies.
What the Active Autowerke Stubbies have accomplished is to transform you existing BMW primary exhaust catalysts into a smaller, more compact unit that has added features. Just by cutting with a sawzall and welding by someone competent, you will have a resized BMW factory catalyst in a much smaller package. Now you can run the Active Signature X pipe on the street or the race circuit and all it takes is switching your front pipe sections to suit your surface conditions. This can be done repeatidly in multiple re-installs since there are no gaskets to replace.
Best of all, your catalysts can now be stored easily in a smaller more modular package.