Sorry.. didnt see earlier...
I have a cap in my system.
Why? Cuz my voltage is not constant and so it helps smooth out the voltage. Oter uses of the cap is to be small additional power storage so that when your system suddenly hits the hard bass notes, it has the additional power availale.
However, there are som epeople who say that caps are a filter which will limit the amount of power to yoru system as the power required will be used to charge your cap first.. but I feel the cap works for my system