Car audio upgrade. Looking for any suggestion and feedback.

Looking to upgrade the sound system in my 08 Hyundai Azera.
Mine is the Limited trim that comes with a 6 cd changer and 10 premium Infinity speakers.

The sound is decent but I have not been overly impressed. No amount of tweaking the fader/balance gives that immersive sound I am used to and looking for.

I am not looking to replace everything but rather make specific/targeted changes that will make the most impact to the overall quality of the sound.

After I started hearing constant audible distortion on the right rear speaker when playing music even at very low volumes , it just hastened my resolve to make the changes.

As with any audio purchase I do extensive research on the web, forums and YouTube to get a sense of what is involved and the components that seem to be garnering a lot of love.

Based on the research thus far I have been able to replace the head unit ( Pioneer DEH 80 PRS )
and the 2 sets of front and rear seat speakers with Infinity Kappa 62.11i.

To say there has been a marked improvement in the overall quality of the sound would be an understatement!
Just being able use a 32GB SD card filled with nothing but music and setting the head unit to random play has been nothing if not impressive!

Now I just use the cd player to audition cds to see if it's worth my time to rip them to the SD card.

Next changes/upgrades I want to make will be:
1. The tweeters. I am thinking of the Infinity Kappa 10.11t unless someone has a different set I should be looking at within the same price range.
2. The subwoofer. Looking to replace the stock 8" that does not seem to dig low enough. I tend to hear some resonance when listening to very good recorded music that can go low. Unfortunately I cannot seem to find any specs on any of the speakers to tell what their specs are. I am not sure I want to put a box in the trunk which is why I would be satisfied with just replacing the existing one with an aftermarket one.
3. Also toying with the idea of replacing the amp with a 4 or 5 channel amp to replace the stock one. Cannot seem to find any details about its specs.

Any suggestions , feedbacks, experiences you can share?
AMP/Pre Pro: Outlaw 7000x, Marantz AV7703
Speakers: Fronts:LSiM 705s/ Center: LSiM 706c / Surrounds: LSim 703s
SUB: Rythmik LV12R x2
Source:OPPO UDP-203