yeah, the lower cats are there to clean up whatever is left over from the cats upstream. BTW, you should replace "many" with "most" in regards to 2000 models.

However, I wonder if the second set of cats will function as main cats? If that's the case then for us 2000 owners it would be a matter of getting two of the cats that go downstream and adding them in. Kinda spendy but maybe doable? If I come up with the money and am ready to buy I'll contact SLR directly and ask how this would work.