Basically (and this should answer both your questions) the coils have 12v going to them fed from the harness at various splice points. The 12v for the coils is shared from one power source and also supplies the ignitor (brown wire, orange trace). However each coil has its own ground wire to the ignitor to contol charge and discharge the individual coil. For reference, the green wire under the connector cover you attach a tach lead for a dyno to is one of these coil to ignitor wires. The MSD intercepts the ground wire for the coil from the ignitor to trigger the box. If you cut the ground wire from the coil to the ignitor, the wire coming out of the ignitor goes to the input trigger of the MSD, the wire end that is connected to the coil, goes to the MSD box coil output. The MSD sends 450v to the B+ of the coil and controls the ground the coil to fire it. Between the wire from the ignitor to the MSD box, you must use a tach adapter box (3 required) to simulate the coil current load on the ignitor so it can generate an IGF signal for the ECM to allow injection. MSD does have a wiring diagram including wire colors detailing installation. They do not provide the specific location of these wires. Its up to you.
What I suspect happened to your ignitor was you either back fed the 450v to the ignitor because you did not seperate the B+ of the coil wires correctly or you connected the trigger and grounds incorrectly. Intercepting the IGT wires which are the ignitor triggers from the ECM to the ignitor will make the system work but overload the ignitor and burn it up. The ignitor will spark the coils but the voltage levels are way higher than it can handle. It will work for a while then crap out.
Hope that answers your questions. Careful installation is important and you MUST make sure you are putting the B+ for the coils ONLY to the coils. I would recommend cutting the wires near the coil connector and sealing the cut end of the factory harness to be sure. Also make sure you connect B+ and ground wires of the DIS 2 to the same coils. Meaning, don't use the power side of the DIS 4 on one coil and the ground wire from the DIS 2. The box regulates the voltage to the coil to make it more stable. Also make sure you connect the DIS 2 to a paired cylinder 1&5, 2&4, or 3&6.
JZ