I worked in a vw franchise for a while and i was always fighting with the parts department over vr6 rear silencers. There is a single piece rear box available. To fit this you cut the rear silencer from the middle just before the rear axle at the point where it is roundest. You will have to buy a sleeve to mount the new rear silencer. This is available from vw and is produced for this purpose. It is the same for mark 3 vr6's, polo,s and some audis. You will just have to get someone in the parts that has half an idea what they are doing! I hope this helps. :D
Riki.