The power rating for the CVR is total input power handling (i guess you could say both voicecoils). Keep in mind though, the manufacturer's power ratings are unregulated (no regulatory commision like with home gear), meaning a crappy company could slap virtually any rating they wanted on the box of their amp. This means Kicker has to make a generalized guestimate on power handling. Realistically, if the amp were clean enough (low THD) you could put a lot more than 300W to it!
The lower the THD (distortion created by the amp), the more power a sub can handle. Stated in simpler terms, if you bought a really nice an expensive amp rated at 1000W, and a really crappy amp that created 250W, guess which one could damage your sub if you decided to test some limits? That's right, the 250W amp. Keep in the back of your head, that distortion blows subs much more readily than power. Or even better, when an amp ceases to create power (maxed out), it starts making distortion.
That being said, i think i've solved one dilema and created another. I say this because i'm not crazy about either of those amps. I have never thought much of Pioneer amps (Premier on the other hand is nice), and the Fosgate amp (while it is a good amp company) wouldn't really be able to fully utilize the sub's capabilities. I sell Fosgate, and while i have yet to play with the P3001, i have tested the 301M (predecessor), and it's ok, but i would feel much better about it, if you had a hatchback (nothing between you and the sub).
Don't get me wrong either will work, but you might be able to find a better deal. I'm sure you have found a retailer or friend or whatever that is giving you these choices, so either shoot me a few other ideas, give me a price point, or buy the Pioneer.
As for the last question, DEFINATELY RCA's via a line level converter (LOC). I don't wish to get into the dynamics of line level voltage (I'm wordy enough as it is :P ), but this is the superior means of signal flow. Don't buy a crazy expensive LOC you should be able to find something decent for 15-25 dollars.
Now, want to sell me a computer, i know nothing about them!