After Market Cat replacements

Any suggestions for replacing cats with after market pipes/exhaust?
Are there products available?
How would the ECU be managed so that it doesn't lite up the dashboard?

ThX.

http://www.stratmosphere.com/a4.htm

These folks handle the Milltek exhaust from England. Simply the best performance available for Audi automobiles. I just installed the downpipes & cats with the full cat back system on my S4. The sound is intoxicating and the performance improvement is noticable.