:) Good questions Stuie
Powercaps are possibly the most unstable source for power. More so in installations where the entire electrical system is run from 1 battery.
I had considerable doubts whether or not to use them in my install and whether the alternator would spend 50% of it's time charging them instead of supplying a better current to the batteries. After some research I was able to come up with a neat solution that makes use of the Powercaps as a Voltage stabilizer rather than a voltage drainer. The poweramps are connected through the caps with 0awg, and when the caps are depleted during those massive bassline drops, the cap terminals supply a direct feed from the battery. When the bassline is not as demanding, the rear battery tops up the cap, ready for another drop. Each cap is connected to 1 monoblock and share a direct feed to the -0v terminal of the battery. (generally lots of voltage instability is created through grounding at the chassis)
The Rainbow comps are awesome! Best i've heard for a long while. As any audiophile would tell you, rear fill is just not needed in a good SQ setup. However, as a matter of personal taste, and the fact that I was planning to use the ICPC to view DVD's, i installed some Pioneer 6x9's for a more realistic 4.1 effect. They can keep up with the Rainbows, but not throughout the entire frequency range. Which is where i've used the active EQ to cut certain frequencies and allows them to step up to a higher volume. The Kenwood Amp sits currently on gains of 2.0v and the RCA feed from the soundcard is actually only outputting 1.8v, so the output is actually "dumbed down" slightly. There is still plenty left in the amp, though i'm not sure the Rainbows will match it that far.
Specifically though, the reason i chose the Kicks in the Rainbow range, were because of the fantastic subs. the TS-W3004SPL i've frequency tested down to 30Hz in a sealed enclosure, and boy did that shake the house! In the car however it was slightly different. The amplitude decreased (possibly due to air pressure). However the subs sit nicely at 36Hz, filling the missed range of the components between 36-80Hz.
There are many better subs on the market, i don't doubt that, but when looking at value for money on sealed enclosures, I couldn't far beat the Pioneers woofers.
I have a frequency/amplitude graph of what the subwoofer is capable of if you're interested?
:)