I just liked the idea of having people in my car and not realizing there are subs in the car, and then turn up the bass when they least expect it to scare em s.h.i.t.less.
you aint gonna scare sh!t out of them, more likely they will laugh at it (maybe not right in front of you, but sooner or later they'll be tallking...) nad tell you how bad it really sounds, and if they are the kind of people who know or care, then they will be pleased to show you up, and probably with something smaller, neater, and a hell of a lot cleaner, but crappy and loud never impresses anybody.
I've heard joke systems with six 10" subs sound so much worse than a properly set up 8"
Is there any advantage to upgrading my factory 6x8's to the Infinity Kappas, I have seen several members mention without a new headunit? Would you be able to run them fully off the stock unit or would I need an external amp?
yes you would definitely notice better sound by putting in a good quality speaker, but if you are not going to run a amp, then i probably wouldn't quite reach for a set of kappa's.
instead i would probably look at a slightly lighter duty speaker like the Infinity reference series, as they are a little less robust, they dont need as much power to play, the Kappa's do sound great, but they do usually like a little more power that what a factory deck can output, you probably would be fine with kappa's if you just replaced the headunit, along with better control of the sound coming out of a HU especially with something like an AVIC.
and i usually dont recommend running a speaker amp like a 4ch off of a factory HU, unless loudness is the only thing you are concerned with (if that was the case, you wouldn't be considering Kappa's), although there is plenty of power, there is also a lot of background noise (static) that you will get because of not having a clean signal to amplify.