Conventional vibration isolation mounts are not as effective as expected since the system/structure to be isolated from is normally not dynamically rigid and has resonance frequencies within the bandwidth of interest. Besides, the low frequency enhancement is a characteristic of the conventional passive mounts. Applying inertia actuators to the attachment plate of the conventional mounts overcomes these shortcomings and enhances their performance significantly. This design concept has universal application since it is applicable to any dynamic system. It allows using the widely implemented vibration suppression algorithms such as the collocated velocity feedback and the filtered-X LMS, thereby simplifying the controller design issue normally encountered in a practical complex system. In addition, it requires very little power and force capacity, i.e., a small percentage of the disturbance force, from the actuators to be effective for frequencies higher than the resonance frequency of the mount itself. In this work, the performance of the 'Robust Passive- Active Mount' on a realistic foundation (a system/structure from which to be isolated) and the performance of the multiple 'Robust Passive-Active Mounts' on the same foundation are simulated. The passive-active mounts are modeled as independent spring-mass-dashpot systems in state space form. The dynamics and the load transmissibility of a foundation are modeled as a continuous system in modal state space form. The mounts and the foundation are then formulated as a coupled system with actuator forces as feedback. The issue of the conventional mounts on a realistic foundation is illustrated first by showing the load transmissibility comparison with a rigid foundation. Then the effectiveness of the Passive-Active mounts, designed by the two commercial-off-the-shelf controllers, for machinery is demonstrated on the load transmissibility reduction at the foundation support (fixed end) due to disturbances from the machinery. A general method for simulating the isolation performance by advanced mounts from an elastic structure has been developed. This method is valid for any combination of multiple advanced mounts at any preferred strategic locations on any structure.