Best sub match for Dynaudio 1.3 SE?

Dynaudio makes a Contour Series Sub that would mate perfectly with the 1.3Se. It's pricey, however, at around 3k new and I've yet to see a used one listed since its introduction nearly two years ago.

I've used a REL Storm III with the Dynaudio 1.3SE and liked it very much.

REL is always a safe bet if you do not have the ability to demo different brands first. They integrate well with almost any system, and are very musical.