The Mk5 and Mk6 chassis are near identical mechanically and I know some tuners (APR in the US, Oettinger in Germany) are using the same suspension kits for Mk5 and Mk6.
I checked the Eibach website for lowering springs and they use the same kit part numbers for Mk5 and Mk6 GTI, although the GTD isn't listed yet. If you're just changing springs you'll probably be fine with the ones for the Mk5 GT TDI 170.
Having said that, and if you're changing dampers as well, I'd always check with the suspension manufacturer before making your decision.