This paper considers the k-set agreement problem in a crash-prone asynchronous message passing system enriched with failure detectors. Two classes of failure detectors have been previously identified as necessary to solve asynchronous k-set agreement: the class anti-leader anti−Ωk and the weak-quorum class Σk. The paper investigates the families of failure detector (anti−Ωx)1xn and (Σz)1zn. It characterizes in an n processes system equipped with failure detectors anti−Ωx and Σz for which values of k, x and z k-set-agreement can be solved. While doing so, the paper (1) disproves previous conjunctures about the weakest failure detector to solve k-set-agreement in the asynchronous message passing model and, (2) introduces the first indulgent algorithm that tolerates a majority of processes failures.