You are moving into the realm of planetary geology VanderL. Maybe I can help here. Although I think what I have written is clear, please ask away if not.
Io just happens to be orbiting at a point just shy of the
Roche Limit". As such, it is already under a great deal of strain and subject to tidal flexing.
To complicate it, it is also in a 2:1 "resonance" with
Europa. Because Io is relatively small, and because it is so close, the gravity of Jupiter pulls on it unequally--such that a higher amount of gravity affects the equator and causes the equator to bulge towards Jupitor. Because Io is spinning, it's equator is pulled at different places, which causes the crust to flex.
This flexing is also strengthened or lessoned by it's orbit, which is slightly eccentric.
Now this flex alone may be enough to cause interior to melt , but it is accentuated by the resonance it has with Europa (and to a lesser extent, the other moons). That resonance also causes Io to flex slightly, in the direction of Europa.
The flexing of the planet heats it, which then melts the interior. Because Io is a relatively small body, it has to find a way to release that heat from it's interior. That way is by volcanism.
In Io's case, the volanism is extreme, because the tidal flexing is also extreme.
In Saturns case, none of her moons are orbiting close enough for the tidal flexing to occur at the same extreme level as occurs on Io. That is not to say that some tidal flexing is not occurring--there is evidence of a small amount of outgassing on Thethus, amoung others.
One premise of the origin Saturn's rings is that an orbiting satelite passed within the Roche Limit, and broke up.
There is also hypothesis' suggesting that Europa's ocean may be partly liquid, or at least slushy, also as a result of tidal flexing. This is why some see it as a good place to look for extra-terrestrial life--tidal flexing may cause the interior to be warm enough to force outgassing, if not outright volcanism. This, in turn, warms the bottom of the ice-ocean and may lead to "smokers", where minerals from within the crust are circulated out into the liquid(y) ocean. On Earth, lots of new species have been found around similar "black smokers".
As for the torus that Io is imbedded in, most of the particles in that torus are compounds of sulfer, and sulfer. These are escaping from Io because of the volcanism. When the volcanoes there erupt, some of the material forming the plume has enough energy to achieve escape velocity--the result of Io's low gravity. It then interacts with Jupitors magnetic field.
The material in the torus is very thin, gossemer really, almost non-existant. It's existance wasn't even known until after Voyager, and at that it was only found by indirect means. So it could not be the mechanism shaping Io's surface.