problem after installing headers

Hey guys,a friend of mine has a 03 M3 SMG.He purchased some headers from ebay and went to install them,he came across some issues with fitment so in the end reinstalled the stock headers.However since he did this the car hasnt ran properly since! It was throwing misfire codes and also bank1-3 rich,bank 4-6 lean.So I went over and took a look at the car for him and it appeared that the o2 sensors had been put back in the wrong holes.we swapped them around and also replaced spark plugs.
After the work was completed,i started up the car and it ran rough for a few minutes then smoothed out and seemed ok.So we went to drive it to get the codes deleted and it bogged out before we got onto the main road,wont accelerate,just all around running like crap.So we couldnt get it to the store to erase or check the codes.No other work has been done to the car and all of these problems started after the header swap.
Any suggestions would be greatly appreciated,we are both out of ideas and cant drive it to get codes checked again.

i had a similar problem, and it may be the position of the o2 sensors if you mess up the position you will have the car running like crap, the plug for bank 1 sensor one needs to be on bank 1 the plug for bank 2 sensor 1 needs to be on bank 2, also check the lines you may have burned one of the lines you need to feel the line.

disconnect one of the sensors and see have code you get if you disconnect, lets say you disconnect bank 1 sensor 1 you should get a code for that bank if you get a code for bank 2 then just switch the plugs, check the lines make sure they did not get burned