I have done quite a few stereo installs, not much with custom speaker setups, but a couple, and I agree, less is oftentimes more. You don't need 20 amps putting out 90 bajillion watts to sound good. I ran a POS Toyota Camry with a class D 2 channel 1200 watt amp and another class A 4 channel 600 watt amp, all powering 2 infinity reference 6x9's, 2 infinity reference 4" rounds, and 2 kenwood 12" subs in a dual port box that I built. The Amps were some no name brand that I ordered and after I tuned everything I was out-sounding a bunch of SUV's with $5,000 dollar systems.
The key is in sound deadening and using quality wiring, having a good tuner is a really good thing too. Of course, any stereo installer worth their salt will tell you the exact same thing so I'm probably wasting my time here.
Oh and I haven't even started the stereo for my S130 yet.