PST's 1.03 Torsion Bars are back in stock

Educate me on the shock dictating the ride harshness. I have heard this stiff bar+'good' shock combo Is not harsh but I'm not following how the shock us going to mellow out a stiff torsion bar/spring. What's the difference between a kyb and a bilstein? I have never owned a bilstein, always whatever was under there when I bought it or recently KYB but have not driven it yet.