It's always a synergy between the hu amp cables speakers and the vehicle acoustics including the damping. Sometimes you hit jackpot. With bright amps and speakers a poor rca is enough to cross that thin line of harshness and being detailed. Like home audio there is no easy route for quality sound in a car. Again, it depends on your expectation about quality.Finally, i changed my headunit to pioneer AVH-A2190BT(pioneer website says it has new pcb layout for low noise). Initially i was frustrated because didn't get the quality i was expecting but after playing with its settings for couple of days i am now very much satisfied.
I had to set hpf for rear speakers at 50hz to remove boom and muddiness, fader to 2 units towards rear, equalizer bass +4 from 50 to 200hz to suppress loudness of tweeter. Most importantly time alignment for all positions (this made the most significant difference, i figured out this very late). There is no harshness in tweeter now, soundstage and vocal texture is very good, bass is very controled and tight similar to my room speakers that have silk dome tweeters.
In jvc, crossover points are automatically adjusted according to speaker and tweeter size selected and there is no way to disable this. I guess the factory settings dont go well with focal components. Tweeter of focal is very loud.