Was interested in this myself so i sent an email off to awesome gti and heres the response i got:
Hi Stuart,
Right first of all here are the list of modifications required to upgrade to
stage 2:
Complete exhaust system with sports-Cat or De-Cat (De-Cat is for off road
use only)
Performance air intake kit
Not NEEDED but recommended to get the most out of the engine:
Intercooler upgrade
Please let me know what you have/haven't got and I will be able to price the
bits up for you
DSG clutch
We have done a stage 3 turbo kit on a DSG equipped Mk6 and never seen an
issue after 20K of hard driving as well.
We no longer deal with APR so it will have to be the REVO tuning but to be
100% honest with you the REVO software on the newer 2.0TFSI and 2.0TSI
engines gives much better increases over APR.
Hope this helps.
Kind Regards
Mike - Awesome GTI Store