Csciam1

I recently upgraded my sound system with 4 Polk audio db 651 and a pioneer ts-swx 251. But I wanted to keep the stock head unit so I used a line output converter behind the head unit. This setup worked great for a few weeks, but now the sound keeps going out. I have twice taken the dash apart to find the butt connectors I used weren't connecting the wires anymore. So my question is... Are there better solutions than butt connectors? I've seen heat shrink tubing and a friend suggested wire nuts. Anyone have any advice? Thanks for the help!