I've gone through numerous audio upgrades and finally found what is ideal to me, with my top off on the highway I can hear the music perfectly, and that also includes a louder exhaust (Banks).
I went with a 7 channel fully active system using two amplifiers and a combination of Polk, Helix and Kicker speakers. The tweeters were relocated to the a-pillars which was a huge upgrade.
Another forum member had a great idea,
@cliffish recommended the below inline tweeters for $20. Those used in combination with your four speakers and new 8" subs, plus a 6 channel amplifier will give you a great boost. I say 6 channel amplifier because you wanted two 8" subs with the standard four speakers, or possibly 6 speakers with the inline tweeters.
https://www.amazon.com/dp/B00HWJTIBE/?tag=wranglerorg-20
5 channel amplifier for one subwoofer.
https://www.crutchfield.com/p_530PN5640D/Soundstream-Picasso-Nano-PN5-640D.html
Unfortunately you will not find an inexpensive 6 channel amplifier, so using a 4 channel and 2 channel would be less expensive.
https://www.crutchfield.com/p_130GMA3702/Pioneer-GM-A3702.html
https://www.crutchfield.com/p_530ST410KD/Soundstream-Stealth-ST4-1000D.html