Well, now that the humor has been nicely covered............
First, your AC sub panel, if it is to meet code, will be grounded to the main panel, but that's not what star grounding refers to.
Star grounding simply means that the ground side of all equipment in a system (or of all devices on one chassis) meet at a single point. This is done to reduce the incidence of "ground loops" inside a piece of equipment, or between pieces of equipment. The word "star" is used because if you were to draw a circuit diagram of such a grounding arrangement, it would look like a star, with all the ground legs radiating out from one point.
In audio, especially in systems where the components are connected with single ended (RCA) interconnects and all the power plugs are three-prong (with ground pins,) ground loops are easily formed. Here's why (in big general terms!): with single ended interconnects, one of the two signal conductors in each interconnect cable is connected to the chassis of the component on each end of the cable. In addition, each chassis is also connected to the ground pin on its power plug.
Let's just take an interconnected amp and preamp OK? Now if you plug both units into an electrical outlet, that means that the ground pins of each of their power plugs are "connected" because the "ground" terminal of all the electrical outlets in the house is the same "ground." So now you have a loop -- in other words the two chassis are connected -- once by the ground pins of their power plugs, and again by the signal interconnects, thus forming a loop!
You need to break this loop to eliminate 60 cycle hum (why is another topic) and you can't break it at the interconnects, or you'll lose your signal. So the only other place to break the ground loop is at the grounded power plugs. If one of the pieces of equipment didn't have that pesky ground pin on its power plug, the loop would be broken; and everything would still be grounded (via the interconnects) through the ground pin on the remaining piece of equipment!
In practice, since all interconnects lead either into or out of the preamp, we choose the preamp to be the only component that's actually "grounded" at the wall outlet, through the ground pin on its power plug. All other equipment uses a little adapter on the power plug (sometimes called a "cheater" plug) that eliminates the ground pin connection to the wall. The equipment is still "grounded to the wall" via the interconnects connecting it to the preamp. So now the preamp becomes the center of a ground "star", the single point through which the entire system connects to ground.
