different, they are 8's, punchy, hard, fast, is a tipical 8, using a ported box should give a bit more out put, but you can never make up for cone area!
I would over power them and leave gain low giving the amp good head room.

 

gain isnt a volume knob...you set gain to the same level as the output of the source unit (whether it be headunit, eq, line driver) volume on eq or h/u is the only way to control volume or how much power is going to the sub. you can reach clipping levels even with gain at 0. depends on source of the music, hu outputs, input power. there are alot of variables. 500 on each should be plenty.

 

i would say 1000watts also, and yes gain is not volume knob, but is does allow you to adjust how much output is going to the speakers, i am not one to buy a 500w rated speaker and put a 500w amp on it, i would put a 750w amp on it and adjust gain back not pushing the amp to is limit, this typically gives you much better sounding and lasting system! Dont get me started on watt raings because there is none standard in car audio!

 

impedence rise has to be calculated for when buying an amp if you really wanna get technical. 1.5 is too small for those subs.

i would go 2 cubic ft air space with port being 32.0 sq in x 21" long. 1.5 would be fine if he was putting more than rated on the sub. which i wouldnt recommend for a daily system not competing. i can make a box for those 8's that wouldnt have them "punchy, hard, fast, is a tipical 8" seen it done already and also have done it myself. 3 8's on a stetsom 2k6d was louder than 3 12" cvrs...all in the build and setup.

 

what would you charge to build him that box?

 

he's tryin to sell subs now...