Thank you very much for the replies. I am going to give a try to Virtual Sound Canvas: I had a SC-88Pro in the past so I am really curious to compare the playback quality between the virtual tone generator and the real hardware.
Update: The comparison against my Roland E-60 is embarrassing :-) VSC is a nice app (at zero cost) but a true tone generator in hardware is all another planet for a serious GM/GS/XG playback, in detail the panning effects were really poor, I have used some J.M.Jarre midi songs for testing where synthesizers voices and special effects are half of the listening pleasure. The results are believable but far from the dynamic and presence of the E-60 sound engine.
I will look forward for purchasing a second-hand tone generator, more compact than my actual Roland keyboard.