You pretty much have to put stock parts on to smog here, so every 2 years thats what we do. On my old A4 I paid my buddy who had a shop $150 to put back stock exhaust, turbo, and injectors for smog and I kept the stock map on file to put ECU back. Had to do that twice during my time with her. Cali is a PITA. Like I said I know my smog guy too, soo we tried to get around it, with no luck.
Most of the catted downpipes have a very small high flow cat, that collects some gases, but not nearly as efficient as a "legal" cat. All your other mods would make it tough to pass too. Your obviously going to be burning more fuel and making more waste than stock. Good luck!
Still love my 4 rings, but now all I see is stars.
White Collar Hippie