Audi A5 3.2 catalytic converter issue

Hi guys, I have an Audi A5 3.2 FSI QUATTRO Tiptronic 2008. I bought it from another country and when it came, turns out it was missing one out of two catalytic converters. The car is loud when revving and the sound is coming from underneath the car in the middle. I have emptied out the second catalytic converter. Now my car has two empty catalytic converters. The sound is starting to bother me, since it does not sound good (like a V6 should) and the sound is not coming from the end of the exhaust and rather the middle of the car. What would you recommend to do? I have tried to find used OEM catalytic converters but no luck since many parted out cars don't have them. Should I put it dowpipes? If so, where can I buy them? Any information would be helpful. Thank you!