Honestly I don't believe in 'crappy' gear. I only believe that you get peanuts if you pay peanuts so all systems are good. Just a matter of
how good they are. Let's just maximise what you have then only talk about upgrading it later down the line. The only thing I protest against is
fakes.
Honestly - forget about the rear speakers. Mine are still stock. If you want (and if your amp can handle it) you can run your front component speakers active (2 channels to the tweeters and 2 channels to the midbass). I'm not familiar with SS amps so I can't recommend what component sets goes well with it. But if the amp is anything like the newer SS characteristics, you'll want to get a component set that isn't 'bright' sounding otherwise you'll pierce your eardrums me think.
Usually the recommended setup is separate amps for sub and front speakers. Preferably a class AB monoblock for the sub and a nice AB, A or hybrid for the front. Class D is ok but I personally don't like the way it sounds if compared side by side to an equal class AB amp. It's personal preference la. Class D is super efficient so amps don't run hot so that's a plus point though. You can pretty much forget about class A and hybrid amps at your 'level' since these type of amps usually cost more than just an arm or leg.
My question to you is what is your definition of "solid and clear sound"? Best for you now (and this is my personal advice) is to go make friends with ICErs, have a listen to their cars and determine which setup you like, then aim to upgrade your car to have similar hardware as them. But also know that hardware is just 50% of the equation (hardware = your car acoustics and your ICE gear), the other 50% is tuning. So you need to either master tuning your own car or find a reliable tuner who knows what you want and can deliver it to you.
But word of warning : Auditing other ICErs cars = poisoning yourself into hating your existing setup.
Good luck!