BMW Repair: High Nox emission problem, nox emissions, o2 sensors

Question
Hello, I own a 1999 BMW 323i with 126K miles on it. My BMW recently failed an emissions test due to high NOx emissions but before the test the service engine light came on. The trouble codes read PO (173,130,170) P1(188,189)and P150. The mechanic I took the car to asked me to change all four oxygen sensors which I did. The replacement parts were Bosch universal O2 sensors for the 2 in the front and Bosch direct fit for the 2 at the back.

After changing the sensors I thought my car was ready for the test but it failed, the service engine light came on again with the same trouble codes. my mechanic says I need to get direct fits for the front O2 sensors for the check engine light to go which will equally enable the car to pass the emissions test.

At this point I am confused because I have no idea what is casuing the High NOx emissions and if using direct fits will solve this issue. Please advice me on what to do..Thank you very much

Answer
Imo, always use direct fit replacement parts. I don't think that this is your NoX problem. More likely the catalytic converters are old and tired. But try the Direct fit for the front O2's cause they are cheaper than cats and they need to be correct for proper operation.
-Evan