What do you feel makes the most difference, a quality 4 channel amp, or a sub. (Keep in mind, I'm not a bass fanatic, I think subs should only fill in where other speakers left off without drowning out everything else.)
Sounds like you just answered your own question.
I was mainly wondering which one I should get first. I'm in school, so not the greatest budget, but I've been curious about how much improvement a 4 channel amp would add over the head unit.
Assuming you already replaced your stock speakers (cuz that is the 1st upgrade that should be made), you'll be happy with amping them as the next upgrade. I did it in a different order (did the sub first - but I like bass). To answer your question, amping the speakers did make a big improvement - cleaner, more mid-bass, louder without distortion.
The amp, which allows you to set the gains to match your speakers, thus enhancing the SQ of your whole system.
Yeah, I've already upgraded speakers and head unit. Sorry, forgot to mention it. I have Infinity Kappa 6.5" component system and Pioneer DEH-5500MP head unit. I already bought a JL Audio e4300, heard it in a friends car and it's awesome, I love the controls and the clean sound of it. Have yet to hook it up, do you think it'll push a kappa component system and kappa 6x9's pretty good?