For each symmetric quiver, Kontsevich and Soibelman defined a collection of rational numbers, the “refined Donaldson-Thomas invariants”. They conjectured that those numbers are in fact non-negative integers, which was first proved by Efimov. In this talk, I shall explain a new approach to studying these numbers, inspired by various aspects of the Koszul duality theory for associative algebras. In particular, this approach leads to a new family of quadratic algebras which are conjectured to be Koszul and are proved to satisfy the “numerical Koszulness” criterion. This is a joint project with Evgeny Feigin and Markus Reineke, partially relying on my recent work with Sergey Mozgovoy.