Probable issue with exhaust system?

What is your question?

Car is throwing code with multiple misfires, we think weve tracked it to exhaust or csts, possibly precat, anyhow im wondering if i put in my code readings and whats been done so far if someone could brainstorm with me to identify the actual source of the problem. I think im getting close but im just not a mechanic.

What makes this problem better or worse?

Runs very rich, backfires, etc.

How long has your 2004 INFINITI FX45 had this problem?

More than a year