Can I place the legs directly on the concrete?

You can possibly place the legs, with regard to contact noise (to the floor below), on rubber mats 1 to 2 mm thick.

Climate-neutral floor structure
FIT - Flanders - State of the Art Agentschap Innoveren & Ondernemen Vlaanderen Circulair  content= Made In Belgium EIT Climate-KIC Netwerk Ondernemen PMV