What happened is that when you regrounded your amp you didnt have it grounded well at first so the amp will start looking for a good ground. It found its next ground through the rcas to the head unit. Pioneer puts little microfuses inside the amp that blow if the amp starts looking for a ground it will protect the head unit. You need to send your unit in and pioneer will fix the microfuse. When you get the unit back make sure you ground ur rcas so if the amp does get a bad ground and goes through the rcas it goes through the ground instead of the head unit so grounding ur rcas does help.