I have read through several dozen exhaust threads and am still a little confused with the options available as far as mid pipes/cat deletes, slip-ons, servo eliminators, duc EE's, etc. My basic question is whether the exhaust valve is located in the stock silencer or collector box? Is it possible to replace either the cat or the silencer without having to remove the servo and cables (hence not having to deal with the error code). Also, I have installed the O2 Optimizer to get rid of the low RPM surging. It works great, but does the O2 sensor go away by removing either the cat or silencer? I read something about a Lamda sensor error code. How is that dealt with? Sorry about the newbie question but I'm just trying to get it all straight in my head.