Removing (all) the cats will most definitely trigger a CEL (speaking from experience). Remove all of your cats (if you want) then use O2 spacers on the back O2 sensors only. They work great; no CEL. The ECU only uses the rear sensors for monitoring pollution control. I have used them on my C32 with no problems what so ever (mine were even home made. Google search it; you'll find what you need).