Jersey, I was hoping you would get a laugh out of that. We have a bone stock D16Y8, the exhaust manifold and downpipe that came with the car, and a stock replacement cat back. The only component of the exhaust not stock or stock replacement is the test pipe... and a small hole in the midpipe near the muffler. I typically don't bother with resonators. Sometimes one can make a small improvement in exhaust note, but usually the difference is subtle IMO. Headers almost always sound better than a manifold to me. Long tubes have a very distinct sound that I personally love on most 4 cylinders, but even short tubes really make a nice sound most of the time. Whatever your setup though, the muffler can make all the difference in the exhaust note. I have been through enough mufflers in my time to know what I like and don't, and what sounds like what. I have a few used mufflers around that I usually test fit to an exhaust before I make a final choice. The wrong muffler can ruin the sound of an otherwise good exhaust system. It just so happens that the exhaust that came on our car has a decent sound as it sits, with no change other than the installation of a test pipe... and a small hole in the mid pipe, lol. For what it's worth, I like the sound of a Flowmaster 40, or better yet 44 on a small 4 cyl. When I redo the cat back on our car, which, by the looks of things will likely be soon, I will have difficulty deciding between a stock replacement exhaust and a custom setup with a flowmaster or the like.
Civickid, I mean no offense, but I do not particularly like the exhaust note of your car. It is not loud or offensive sounding, but to me it is not as pleasant as some others. It can't exactly place what I dislike about it, except that it sounds sort of flat. The biggest problem with trying to perfect exhaust sounds, I think, is that everyone has their own preferences. What one likes, another doesn't. It is no different than music. There are many different sounds for a reason. Each one is unique, and sounds good in its own way. Civickid, if you want a wideband there are some options much cheaper than $500. You probably don't need it for your application though. I don't mean to derail your thread. It sounds like you are on the right track with your exhaust. Someone else will hopefully chime in with some specifics on your primary O2, where to put it and why your CEL is on. I'm with Jersey on putting it in the collector. That is normally where you see them and it works well. It is better to take a collective measurement of all the cylinders at the collector than to base the fuel/air mix of the entire engine on a reading taken from one cylinder, as would be the case if the O2 was installed in a runner. Having a bung welded shouldn't cost you much either.
....It sounds REALLY nice with just the axleback, here's a video...there's also one without the cat on my channel, I bet you'll like the stock headers better! let me know