Audio system upgrade

[dr. d]

Sir replacing the HU is not an option. Some settings of the car is there so...

Sadly, a proper sub is also not an option due to space constraints.

Just looking to improve a bit on the parts that i mentioned

what is currently on board, so's the advisers will not recommend them to you, as are not happy with them...
i'm not an audio expert, but i think that great components may not sound great, if they do not match each other...