It sounds like your Xtant is a 5 channel...
Amp front 6.5" in fully deadened doors, and run sub. That's all you need. I know no rear fill might sound a little odd, and it does at first. My first week without rear fill seemed odd, but since then i have grown to love it. The key is to get the comps to play low enough and the sub to play high enough (read : trial and error with xover settings) so the sub "blends" with the front stage. Blending makes it seem like the mids are playing the sub-bass frequencies, and once you have achieved it, it is bliss.
Amp front 6.5" in fully deadened doors, and run sub. That's all you need. I know no rear fill might sound a little odd, and it does at first. My first week without rear fill seemed odd, but since then i have grown to love it. The key is to get the comps to play low enough and the sub to play high enough (read : trial and error with xover settings) so the sub "blends" with the front stage. Blending makes it seem like the mids are playing the sub-bass frequencies, and once you have achieved it, it is bliss.