The aftermarket muffler (post-CAT) can pass the smog check, the Catalytic Converter however must be OEM. Also, since the check engine light is now on, after installing the OEM CAT you'll need to clear your Acura RSX's trouble code(s) and ensure the code(s) do not return. You'll also need to drive your Acura for 1-2 weeks (apprx 200 miles) in order to "complete" the emission monitors. Clearing the trouble code(s) will also erase the emission monitors, and your Acura RSX can not pass the smog check with "incomplete" emission monitors.
An inexpensive trouble code scanner will indicate which Monitors are complete and which monitors are not.
