What are you trying to acheive?
Louder, clearer, bassier, fuller?
I'd personally go for a seperate sub and amp but something low powered and punchy as you might over bass it otherwise. I do love my bass though so you might be ok without it.
If I was replacing speakers tbh I'd just buy comps and replace the speakers as tweeters are just as important and add to the woofers.
Rca's are better but if your keeping it low powered you should be ok.
Whats your budget? Legatia l8's