Ah okay. Thats no comparing to mine downpipe (catless). Comparing to see is the o2 sensor spacer working or not i mean.
But if you already plan stage2, you can fix the o2 sensor issue directly in software. Or you want first to test it with oem software?
Yes, JB4 is a performance tuning box. One of the best I tested by far.
I have it installed on my Audi S3, Golf R and Clubsport, and just remove it before taking the cars to dealer. It has never been detected as it does not leave any trace in the main ICU.