I bought the Fosgate T1 5.25"s. The basket was too wide for the hole so I had to create a little gap with some spare mdf.
As far as the Kappa's, they're just general replacement speakers. As far as helping you, Clutch was spot on asking for goals. Yeah the sub stage can cover SOME mid-bass. But we don't know if you are just looking to step up from stock, basic replacements, boosting your current vocals, willing to amplifier them, prior experience and willingness to fabricate up a general bracket, etc.
For that price, you could look other routes if you just want to run them off of the head units 15 or 16 watts. It'd just be wasting some potential. If you are amplifying them though, you'll want to run some new wire through the door grommet while you have the door panel off... Lots of options... lol