Exhaust question

[Stanley Rockafella]

On many replacement exhaust systems (including the "factory equivalent" systems), the cat converter seems to be taking the independent dual setup of the e30 M20 B25, and making it into a 2 into 1 setup. See the links below:

Here's what stock looks like:

http://www.bmwmobiletradition-online.com/bmw/showparts.do?model=1113&mospid=47309&btnr=18_0170&hg=18&fg=05

Here's what that p/n shows with google search:

https://www.bavauto.com/bmw-catalytic-converter-bmw1409

the image looks similar to the one in the first link, but when searching google for that pn, it looks like a 2 into 1 setup like the one below:

https://www.amazon.com/Dec-Catalytic-Converters-BMW1409-Converter/dp/B006XXQHGO

My question is, is the setup in the stock system any different than the replacement? or is the stock BMW one simply a 2 into 1 that's just disguised as a dual setup?

Also, should I be concerned with a 2 into 1 setup? My cat is pretty rusty and in need of replacement. I'd like to stay stock, but don't want to waste$$ and time on something that's not going to perform or sound stock (I'd like the replacement to sound similar. I don't have a race car, nor do I hope to make sound like one).

thanks in advance.

[lukeADE335i]

I don't think the 2 into 1 into 2 is much of a problem providing the 1 is around 2.25 - 2.5 inches.

The collar that appears to go across the two pipes in front of the cat in the stock photo actually covers an X-pipe, so the stock system does merge then split again.

[e30strokr]

the only benefit is the car will be lighter with after-marked Cat.. the type of muffler will take care of the extra noise

[McGyver]

I have one of these CA-legal aftermarket exhausts on an otherwise sock car (see pic) and it's a little droney. The other thing to consider is that a factory BMW cat is good for 20+ years on a properly functioning engine. I hear a lot of stories about aftermarket cats failing CA smog after 1-2 years. I think there was legislation in CA to mandate they companies offer an "x" year warranty, but I don't remember the specifics.