No option suits my system .
My head unit is a factory optioned Alpine unit with the word "N'fit" (Nissan Fitment?) written on the head unit, 11 band graphic equalizer, remote, speakers and speaker grills. As the head unit and digital equalizer are still working properly i have left these alone. But i replaced the 10yr old speakers with Hertz compition speakers, consisting of 2-way co-axials in the doors and 6" mid-bass woofers in the parcel shelf. Have also installed a four channel amp to power these speakers, as the factory unit did not have enough power output. Installed a gel-cell Optima battery, but this was done for other reasons not just audio.
I found the Hetz mid-bass woofers to be great, giving that thumping sound/feeling without the added weight of a sub and box.