That's a nice setup. The little H-pipe is nice and small. I believe that I just read that @OCCoupe did something similar with his exhaust setup. Anyway, I talked to the header shop and that have done absolutely nothing with my headers. I'll just chalk it up to free storage. 
Thanks fo rthe tip though, this gives you an idea of where BMW places the 02 sensor relative to the cylinder head:
Thanks fo rthe tip though, this gives you an idea of where BMW places the 02 sensor relative to the cylinder head: