Tuned Mass Dampers (TMD) have extensively been used to successfully mitigate narrow bandwidth type loads of linear mechanical systems based on an optimal tuning frequency. Nevertheless their effectiveness to control structural systems subjected to broad bandwidth seismic type loads is still dubious, mainly because these structures are particularly designed to withstand nonlinear behavior which presumes a mistuning effect of the structure-TMD system. There are some solutions that have been developed to counteract this condition, modifying the passiveness of the TMD to an active condition by adding supplemental control devices. This investigation presents an effective and optimal solution to keep the passiveness of the system. Previous investigations have identified that a large damper-structure mass ratio is more effective when the nonlinearity of the structure is considered, and the optimum way to deal with this condition is by sub-structuring the system subtracting the TMD mass from the structure itself. A simple way to achieve this concept is by optimally isolating the roof of the structure. The optimum parameters of this flexible interface such as the damping ratio and the tuning frequency are studied conceptually through two stages. The former is focused on nonlinear single Degree of Freedom (SDOF) systems. The latter is extended to nonlinear coupled 2-DOF systems in order to consider the torsional condition. Results show that large TMDs are a robust solution to enhance the seismic performance of nonlinear structures achieving not only the torsional balance condition by reducing deformations and annihilating the torsional response but also attenuating structural damage.