Need help...I would like to connect ( Takamine TC132SC with cool tube preamp) + (acoustic takamine DI ) to computer to use (guitar rig 5 presets) with an exit to the Marshall AS50D acustic amp. How to do this? do i need Audio Interface for example (Focusrite Saffire Pro 14 Firewire )

You need to go to the recordings forum & read the stickies, but the Focusrite is the right sort of thing.
USB to 1/4" plug cables are available. I originally used the one from my Rocksmith video game until I got a better one.