I installed a Sony XAV ax-100 aftermarket headunit in my 2008 ES to replace my base non-nav system and have since been having issues with it interfacing with the stock JBL amp. Upon start up, the amp isn't allways triggered to turn on leaving the headunit functional but with no sound coming through the speakers. Sometimes If the amp does turn on I will lose the ability to adjust its volume through the headunit mid-drive while other times the system works flawlessly. I suspect this might be an issue with the amp interface and have been working with technical support to sort out the problem with no luck thus far. Is this possibly a headunit ground issue? Do I need a replacment amp interface? Has anyone experienced anything like this or have any advice?