I'm driving them from an Alpine W407BT Headunit. 4 x 50w is plentyExcellent post! The real question is do they sound any good? (are you driving from the headunit or an amp?)
I've disconnected the stock rears as they sound pants, muddy the mid-range and throw off the "staging" (which isn't ideal in my setup anyway). I imagine the difference is night and day for the highs, but I don't expect you'll get many lows with a woofer cone that small.
Curious also where you found the 8cm drivers - have searched but haven't come up with much in that size.
I've set the HPF on the rear channel to 80hz as the JL 16cm in the front give plenty of bass, the sound is so much clearer now. I ran one original and one kappa at the back and and flicked balance left to right and the difference was stark. Only problem now is the dash tweeters are struggling a bit. Once those are sorted I'm done, I don't think Ill need a sub, the JLs get the wing mirrors vibrating nicely :lol:
I was lucky with the 8cms, just did a search on ebay and they came up, got em for £35, not bad for infinity Kappas!