W/ only 1000watts RMS, u could either get two decent subs powered well, or one good sub powered to RMS ratings.
Depending on space, you might want to only do 1 15, i really underestimated how much space my 2 15's took up.
I'm running about that same type set up tho, I have two powerbass 15's xxl
THeir 500rms each, and they sound real nice after being broken in. I originally thought they sounded a bit too crisp, but thats gone now //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif.
I would say the kicker CVR's, but I been told they fry easily, dont know how true that is.
A small step up would be the L5 15's, and even those you would be underpowering, which isnt too bad, but wont be nearly as loud as they could be.
But with that much power ur kind of in limbo.
Idk too much about hifonic's amps, but maybe u can strap another one on there?