Alright so I believe I have found a little trick that helps cope with the variable voltage alternator controlled by the on board computer. The cars stock negative battery cable runs through a sensor which monitors the current being drawn which tells the computer how hard to run the alternator. Through out my spl build I had one issue when I replaced the battery under my hood, it was that I could not figure out how to get the factory ground cable out of the sensor. I sat down and figured it out and removed it and ran my 0g ground as well as the small ground ground wire that was attached to the factory battery ground through the sensor. Now my idle voltage is 14.9-15.2 cold and hot, and at full tilt with a 10,000 watt sound system I drop down to about 13.5 at idle. What inspired me to do this was at my last car show I was sitting at 12.5 at full tilt and not dropping nor gaining any voltage, the alternator simply wasnt charging.
Here is a picture to help you visualize what I am talking about.