Question about Walimex pro per LED Sirius 160 Bi Color

This is an area light, which emits soft, diffuse light over a relatively large area. To be honest, I don't think there is a softbox for this. That would be double. There are many other products from Walimex with an even larger surface and correspondingly softer light. Don't forget the distance! If you move the small flat very close to the subject / model, it is a large surface. Relatively / in proportion. Distance is just as important as size

None. If you want to mount softboxes, I would recommend lights with Bowens mounts. E.g. from Godox.