Question about using DSP unit with an Eclipse 8051

I picked up an Eclipse 8051 brand new in the box a while back and I have it installed although I am also wondering if I found an Eclipse DSP how the sound would differ. Assuming it is compatible with this unit. I understand it is there so you can tune it perhaps is that correct? I have a 99 Miata and it has stock speakers that I want to change out. I am just into the old school stuff (Eclipse, MB Quart - that you can't find anywhere pretty much). But I would like to install a DSP unit if it will improve my sound. I am currently using a Eclipse AMP 50x4 that is over 10 years old as well.

Is it true that the newer head units they sell nowadays all pretty much have a built in DSP?