Well.. Other than the obvious difference in midbass size, the other thing is that the 6.5" seemed more efficient to drive, being rated at 1.5dB more than the 5.25" set.

Other than that, I would say, if there's no issues with the mounting depth(since the 6.5" set has a few milimeters more of mounting depth), go with the 6.5" set as generally, you would need a bigger driver to deliver midbass that integrates better with your subwoofer(if you had one, even if you don't, typically a 6.5" would be able to go lower to compensate for the lack of a proper subwoofer unit). 5.25" would usually deliver slightly better midrange and lesser midbass but it's not always the case though.

As for your question of what amp, I would rather ask back, what's your workable budget, and also why would you need 2 sets(I know, you'll probably answer with "front and back")? What car are you driving? If it's a normal sedan, I would rather say put the budget into getting a proper subwoofer instead.

This post has been edited by GRexer: Jan 14 2012, 12:09 AM

Depending on how much power your amps are drawing but I really think you should upgrade considering that power cable you're using is actually only good enough for the active subwoofer.

Well... Just a tip, at least get a 4-gauge main cable going to the rear, into a distribution block, then from the distribution block, 8-gauge to your amps. Should be enough for most normal setups.