Not quite sure what you mean about smarty pants users. Apparently you're a user now, and I never thought of my pants having any smarts. Kinda confused on that one.
Primary oxy sensor is on the front side of the exhaust manifold/cat converter combination.
Mine is originally a 5-spd, has a 5-wire sensor. I've read that autos and/or California HX's had 4-wire sensors, and no lean burn. So don't necessarily blame the previous owner. If the computer isn't set up for lean burn you won't get LB, regardless of your oxy sensor. Sorry I can't provide more specifics because I don't know them.
If you put in a proper HX 5-spd it has taller gearing than other Civics, though possibly the DX and CX have the same tall gearing. So you do have some benefit there even if you don't have lean burn.