I have spend more then 50k easily on Cultus and I still don't like the sound in it.
And I think the original factory sound was better. The best thing you can do is add a branded head unit, Pioneer/ Kenwood etc. Then change the speakers or add ons.
I replaced the head unit with Nakamichi android, added speakers, a amplifier, Dampening sheets.
It's just loud, no quality.
I might change the headunit too, but for now I'm more inclined towards the android rather then sound quality