And also the fact that the subwoofer is actually needed to fill up the last octave of the music spectrum, well, at least, in most of the songs i listen, even crossing my front components at 63Hz doesn't help, definitely need the sub to fill up the rest of the low end for a fuller music experience. Most front components wouldn't be enough to cover the subwoofer part most of the time, even if you are running a 3-way with an 8" subwoofer(which, most, doesn't really have much sub-bass, except, i think, the JL 8W7 and i doubt u can fit the 8W7 in the doors anyway) in the doors

Hehe... one of those songs that sucks without a subwoofer I had been subless for quite a while earlier on, and recently fitting a subwoofer back... i really appreciated the extra octave of music reproduction

Yes, output level/impedance does make a difference. Output level higher meaning you can set your gains lower at the amp, thus reducing the stress on the amplifier, though, it doesn't necessarily means better SQ from it. Just that with a lower gain, it'll usually reduce floor noise.

As for output impedance, the lower, the better as the signal have to go thru less resistance

Great info there driftmeister, it's the first time i heard that output voltage has nothing to do with amp's gain though

Just a note that having higher output voltage has anything to do with getting more power into the amp, it'll only let you set lower gains and thus making the amp work less hard.