well the problem I am seeing with OBD2 is that, the ecu uses sensor input to adjust your fuel trim, to try and adjust it to stoich (well honestly in a honda, a little rich). So running on bad o2 sensors could totally negate the benefits of having the high flow cat... Running with the sensor out of the pipe, again it's going to screw with the OBD2 using sensor inputs to run the car properly.

OBD2 learns, and has a memory, reset your ecu, see if it runs better for a day or two, until it relearns it's naughty behavior.

I just unplug my ECU for a couple minutes, but you can just pull the ECU fuse, or pull the hot battery terminal for a couple of minutes.

Mind you, method 2 and 3 from above will reset a factory radio, and you'll need the code to unlock it.

-PHiZ