The GTI SuperPro ALK kit fitted my Passat arms no problem.
If the hexagonal end of the B6's arm is slightly chunkier than the GTI's steel arm, you wouldn't notice it. Poly and rubber bushes have both needed hammering on to steel and alloy arms. They're far from a slip fit.
Thought I had responded to this… hex ends definitely slightly bigger on B6 arms. There is a definite difference to how bushes slide on, and mine were genuine arms.
I think everything can be made to fit, just that in my case I didn’t want to go that way.
The reply that I thought I had posted also said that in my case I suspect low tyre pressure and wet roads were the primary contributor, rather than softening of bushes that were less than 1k old. Pressures back up and all fine!