fitted a pioneer underseat sub a few weeks back, also running pioneer direct replacements in the front and replaced the backs with pioneer, over all a good upgrade the sub gives enough bass to stop the system sounding flat, to be honest its more bass then i thought id get, in all thou, the whole upgrade cost me about £300 (sub/speakers). the sub also comes with its own wiring loom which i thought was cool, with some drilling the brackets with the sub fit perfect to the seats brackets.
heres some pics of it fitted
heres some pics of it fitted