S80 T6 O2 sensors and catalytic converters

[Fradog]

(2003 S80 T6) Recently had cyl no.s 4 and 6 ignition coils quit. Unwisely drove it home about 10 miles. Replaced coils, no problem there, but then got a p 430 error code (cat threshold efficiency bank 2). Started simple, looking for vacuum leaks as suggested by local Volvo independents and discovered a small crack in the charge air pipe. Glued that closed even though I believe that would not cause the code. Still got code after a few driving cycles.
I assume the unburnt fuel that may have been fed into the cats could have ovheated them. I say may have because I would think the system would have shut those injectors down when it detected the misfire.
Anyone know if it can do this?

Pulled off the cats (as an experiment to see how much trouble) and found no big rattles but there is a fair amount of sand like material that will shake out and looking in the end of the last big cat it's grid appears about 30% filled.
Is that enough to say it is done?

I will probably get new o2 sensors while I'm at it but one big snag: I can not find the connectors for the upstream O2 sensors. If they are where I think they I can not see them or reach them.
What is the trick to locating these darn connectors and then getting at them? (I have access to a lift.)

Thanks for any help.