exhaust sys. ???'s O2 sensor

[s14slide]

well I've searched this forum high and low and have yet to find an answer. On an s14('95 specifically), w/ a hotshot header, high flow cat and cat back, how important is the second O2 sensor? Does it have to specifically be put in the exhaust stream after the cat, or does it matter? I've heard that it has to get a reading after a cat and that w/ it either not hooked up or hooked up before the cat, you'll get a lean mix which will rob power and cause engine damage and also get that damned check engine light. My headers did not come w/ a provision for the second O2 sensor. Again, this is all hear-say info and I'm hoping someone w/ maybe an FSM will be able to answer my questions. Thanks in advance.
And Happy New Year's.
This year call's for a KAAZ and a set of FLT-A2's. Wooohoooo!!!!

Edit for grammar and spelling.