Hello everybody. I have the same problem (1998 LX) and I think it's most likely the cat as the ECU indicates. Through some research on the net I found this TSB which might aid you as you mention the coil. It involves crimping the connectors at the igniter terminals.
If it was the sensors it the ECU would throw more codes. I have an aftermarket 2 piece (flanged) exhaust manifold / catalytic converter and I myself am wondering if this two piece is better than a one piece unit. I've also heard of a bad ECT (engine coolant temperature) sensor that could throw this code but again wouldn't this throw a different code?