Why have you got a wrong signal from the rear O2 sensor? Is the sensor tested as being good and is the cat working?

I went through a spate of these FTO's a few years ago. I had at least two with similar symptoms to yours that needed cats and both had an underlying rich fault that killed the cats. Mine were bad maf signals due to rotten wiring under the air filter but yours may be different since you mention that it has a map.

Edit to add. I think you will find the car is a 2.0 rather than a 2.5 and a quick google will turn up loads of workshop manual pdf's.