Never heard the Kappas but I have heard around the forum that they have harsh tweets. I've also heard they aren't much for midbass. I have heard the REVs and the tweets seem to be ok. The 6 1/2" revs have some decent mid bass for the price too. The perfect solution would be to listen to both but we all know thats hard to do most of the time.
ive got a set of dp601's for the front, and im very impressed with them. very clear high's/aswell as having fairly decent midbass. not earth shattering or anything, but they deffinetly do the job well.
give them some external power, and the'll really shine //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
btw, i got my set of ebay for 55bucks //content.invisioncic.com/y282845/emoticons/greedy.gif.5a53e6246569d7ab79867170f3b06629.gif