I have a different opinion. 1 1000w amp is better than 2 500w amp. First of all, 2 amps will waste more power, and secondly, it'll generate more heat. Not to mention you'll need 2 pair of power wires, rca cables and cargo space. So you can see, there's nothing efficient about it. With multi amps, you also increase the chance of getting ground loop. The only thing positive about owning 2 amps is, if one fails, you have a backup. That's about it (2 amps cost more than 1).
I doubt that isaac..ive seen hundreds of jl 500/1's with the same operation as mine. Ive seen 3 or more in most cases of either multiple 500/1s,1000/1's,300/2's in most high end sound systems. As long as the installation is done the right way. I doubt youll have any problems. Jl's tend to be more efficant then most brands anyway.
MO, you might want to test it for yourself then. Get 2 or 3 JL 500 and 1 JL 1000. Apply same amount of music power, then measure. You will notice the extra current draw, and heat, not to mention all of the extra work/space needed. If amps were made to be 100% efficient and perfect, then yes 2 amps will equal 1 higher amp. But that is not the case. Let's say each 500 amp when idle, uses up 1.5A. The other 1000 amp when idle might use 2A. If you add up the numbers, you can clearly see 2 amps will use up more power. That's what happens when you have multiple power supplies. You have to remember, powering 2 500w subs with 2 amps vs 1 1000w amp makes no difference in sound quality.
Maybe not in sound quality but either way its not gonna hurt.. LIke i said before isaac. I am running 2 jl 500/1's and the ppi art 300.2 i got now. SO you do the #'s.. I doubt there will be any problems if the install is done right with the right stuff. Doubt it..lol