Simulations of digital systems has always been a challenge, when the added complexity of analog systems is inserted into the simulation, it becomes extremely difficult to simulate the entire system in real time.
I'm afraid it is more of a limitation of the host system, then the simulation software.
Notice if real time simulations of digital hardware are required, they are typically implemented on a FPGA platform, not emulated on another processor/OS system.
As the clock/timing of system under simulation increases, the analysis time quanta decreases to a point it is no longer possible to simulate the multitude of simultaneous/concurrent events in the given quanta.
Therefore this is why a digital/analog mix system which can be simulated in "real time" in the kHz range, cannot be simulated in "real time" in the MHz range.
BigDog