Hi have a Marshall DSL 401 amp and an ampeg svt-3 bass amp and would like to connect them to the computer thru an audio interface

The marshall amp has a port for DI out..is it ok if i use this to connect to the computer

for the ampeg amp it has a balanced line output and preamp out...which one should i use..

as for the cable...is it ok to use instrument cable or should i be using some other cable..
Instrument cable is fine, use the preamp out on the SVT and see how it sounds, it should be fine. The DI out on the Marshall should be good too. What interface are you using?
Telecaster - SG - Jaguar
Princeton Reverb, Extra Reverb
P-Bass - Mustang Bass
Apogee Duet 2 - Ableton Suite