Well I tried to fit my K46 exhaust system to the K67 and unfortunately it doesn't fit. So I have ordered the Ti Akrapovic copy from Aliexpress. £270 including shipping. They also agreed to ship at lower value which was welcomed. The interesting thing is that the O2 sensors are located further back on the pipe, compared to oem, which might prevent the O2 failures.
I also looked at Black Widow exhausts and their down pipes look like a copy of the Arrow system. The only negatives is that they don't do Ti and the front O2 sensors are more forward than the oem system so therefore O2 failures may be more regular.