You need an instrument fitted with a hexaphonic pickup, like the Roland GK-3B, and a device to convert pitch and velocity to midi notes for each string simultaniously.
The GT-10B is only a multi effects unit which inputs an ordinary mono analog signal.
The GT-10B has USB to carry audio to/from the GT-10B, as well as midi control and system exclusive data.
I have used pitch to midi software on a computer, with softsynths, and used the GT-10 expression pedal to control the synth levels. And have the bass signal go out the USB to a laptop using pitch to midi, then into a softsynth, then back out the USB to the GT-10B.
It worked ...O.K..... but you are better off with some thing like this
The new Roland GR-55
http://www.roland.com/GK/GR-55.html