I wouldn't even bother with the harness. Just cut the connector off and solder the wires directly to the new speaker. Less resistance.
Kicker speakers... I wouldn't buy a Kicker component set for the front but they might work as a good speaker for the back. They do produce good bass for a 6.5" (With an amp) I run Focal K2P in the sound bar. Anyone you talk to will say you can't put Focals in the sound bar but it can be done. : ) If you decide to go with something with a deeper magnet it will take some customizing. They will have to be ported as well. The end result can look stock.
Infinity... Kappa's are good, Reference (The line that you see in Best Buy, etc.) are not too great. I prefer Focal, MBQuart or Bostons.