Hi, I recently went through the same ordeal. I prefer clean, bright audio. I went with Boston Acoustics FX3 (3.5") in my front dash, BA SL65 (6.5") on my front doors, and BA SL95 (6x9) for my rear dash. I have an Alpine CDA9827 deck, as I wanted to avoid motorized faces. (Not a big fan of them...personal preference)
Anyways, I have a single JL W3v2 (dual 4 ohm) hooked up to an Alpine M501 550x1@2ohm. The bass is VERY tight and deep. It hits extremely low and is MORE than enough for my 2003 Neon SXT.
What kind of car is this stereo going into? That is the main factor. Something bigger, like a SUV, would need 2 subs.
Anyways, I'd recommend running 500W+ to each sub, assuming he's sticking with the W3 series.
If he's looking for just a lot of bumping, I'd get that amp you are looking at and a pair of JL W0s in a bandpass box. HUGE bang for the buck on those subs. They need next to no power to run, either.