^ I had bad experience with Kenwood (from the cheap part of the line-up, and about 4 years ago). When I experimented with my setup, I wanted to put tweeters and mid-bass through separate amplification channels (with active crossover before the amp, dumped the idea later), and tweeters were incredibly noisy from this amp. Also when I powered subwoofer from it, it gave quite a loud "boom" impulse on power on/off.
Since then I was using Phoenix Gold, and I couldn't be happier. True power is much more than what manufacturer prints, and quality is all I could ask for. Plus it has those great 24db/octave crossovers, so my sub is not producing any high notes and delivers the punch where it's needed
But again, it's quite noticably more expensive, so I can't say all PG are better than all Kenwoods, but that's my experience.
For a cheap setup I can recommend 2-way system powered from head unit + subwoofer bridged over 2-channell amp. That way you can always expand the system, say connecting your speakers to this amp, and buying something more powerfull for sub, or if you buy another sub to pair with this one.
Just remember to do all the sub-box calculations if you plan to do it yourself, don't blindly follow manufacturer's recommendations, they often sound bad, and are tuned for high SPL (I like my bass, low, not loud). Or you could just get an active subwoofer, they are ok (some are very very good), if you don't need scaleable system, or just not interested in subject.
Don't bother with expensive speakers for back, all the important sound should come from front. Especially highs. That's why 2-way is needed, to place tweeters on dashboard, and orient them to get a uniform stereo-picture. 3-way is just too much work to get it sound right, and a newbie can easily make it sound worse than 2-way.
) Keeping that in mind I wouldn't spend a fortune on components such as amplifiers and subwoofers any more...
