Recently purchased slightly used RBQ w/Infinity to replace stock single-disc and four speaker combo... Few questions... Easiest way to remove dash to access speaker mounts for the three that go on top of dash-board?? Are they pre-wired?? Door panel removal, any tricks to make it easy?? Will existing plugs from current head unit work with the RBQ, or do I need to change out?? Any advice appreciated in advance, THANKS...