Putting a pair of Polks with > 75 RMS will be amazing. They handle 100W RMS. I have had different ones from their DB series and MM series 6x9's, 6.5's, Slim 6.5's, 4x6's, 5.25's.... they're all fantastic for the money. Even their subs are surprising especially the MM subs. Getting a set of 6.5's for the rear doors and a set of 6.5's or 6x9's for the front doors and replacing the dash with a set of tweeters or another small speaker will be loud and clear. The Polk 6x9's and 6.5's put out a surprising amount of bass too. Infinity Kappa's were always lacking in bass, and overbearing in treble. Their Reference series sounds much better.