Here is a full shopping list and final total for how I seriously upgraded the 430N "premium" sound system in my 2013 JKU Rubi while retaining a totally stealthy & factory look. I installed the speakers and had the amp & processor installed professionally. The sound went from pitiful to very loud and satisfying, with remarkable bass out of the 8" factory enclosure, and fairly minimal rattling at high volume. It ain't cheap, but when you figure a tricked-out replacement head unit (to say nothing of the other toys) is around $1K, I think I did pretty good.
I did this in stages. I put the speakers and polyfill in first. Sound was better, especially in the sound bar, but overall improvement was marginal. If the factory system was 1 on a 10 scale, the speaker replacement took the system to a 2. The addition of the processor and amp took it to an 8/9 in my book. Coming from a pretty serious car audio tradition back in the day, I only reserve 10 for outstanding all around sound that comes with in excess of 1K watts and some serious sub enclosures, plus higher end speakers (the Polks are very good, but not stellar/great).
* Polk Audio db6501 6-1/2" Component System (dash): $199.99
* Polk Audio db 651s 6-1/2" Slim 2-way Speakers (sound bar): $49.99
* Outlet Special: Polk Mobile Monitor MM840 8" 4-ohm Component Subwoofer: $161.49
* JBL MS-8 Processor: $499.12
* JL Audio XD700/5 amp: $379.98
* Stiner 12ft 4000 Series Professional 6 Channel RCA interconnects: $25.69
* DB Link X-Treme Series XK10Z 10-gauge amp installation kit: $19.49
* DB Link PK4Z 4 gauge power series amp installation kit: $30.15
* RCA AH16100SN 16-gauge speaker wire (100 ft. for $10.48, but ended up buying some “nine wire” cable from the installer for a cleaner look)
* Black Speaker fabric and pet netting to cover it (latter gives a more rugged look), some wood to cut out a new grill, and some Velcro and staples to bond it all together. The velcro lets me take the grill on/off: $20 or so
* A pillow for polyfill $4 or so (stuffed it liberally in all the speaker enclosures)
* Adaptor for sound bar speakers because Polks were too small (UPC 086429029822): $18.99
$400 (included $40 or so for "nine-wire" replacement speaker cable)
GRAND TOTAL: About $1820
p.s., processor went under front passenger seat and amp went under passenger side of rear seat.