Pretty much plug and play. Match the wires of the harness to the aftermarket HU wires then plug in its sockets to the factory plugs/sockets and plug in the RCA's. The RCA's are the ones that powers/controls the factory sub/amp.
It's not going to give you "Mega Bass". This is because it's a factory sub and since it's still working with the factory amp...the nice thing about it (at least on my 02 with a Sony HU) was that the Sony HU I had in it has a separate BASS control for the "SUB" which Sony and most name brand HU's will have directly related to RCA out's. This "Sub" bass control gave it a bit more "thump" than factory when I put the control level at + 4, above that and the factory sub sounded stressed, ready to blow.