My understanding is that which ever cat the OBDII sensor is sitting behind is the primary cat. Many cars have close coupled cat as their only converter because thats where the temp is the highest and the conversion is most efficent. The second cat on the Protege is only considered a polishing cat for ULEV status.
Razor, if you want one contact protege5online.com.
BTW my CEL started coming on a little too regular so I installed the filter I explained above. It took it out for good. I was wrong too, it cost $2 for parts.
the primary cat is always the cat that runs hotter, hence, the primary cat AND Pre-cat are the same cat. The one cat just off the downpipe is the secondary cat. Primary cat is the one integrated into the exhaust manifold, which is what the header replaces when you get em. It all becomes obvious when you take off your exhaust manifold heatshield, you'll see it, looks like a keg.