To enter the Sith Base after by interrogation, you'll need to convince the prisoner at area #7 to talk. You can do this essentially by choosing the same options one or two times until he spills the beans. You'll be talking to the Intelligence Officer to begin the interrogation. Here is the general sequence you'll use to break the prisoner.
1. Choose the "Relax, I'm not here to threaten you" option.
2. Choose "We're the only ones that will take you in now."
3. Choose "Let's try something else."
4. Choose "We know something about your companion."
5. Choose "Perhaps we would give you back to the Sith, but keep him."
6. If it fails by this time, try the same course of action another time, using the "Maybe we should do something about Tela" line as a substitute for #4, followed by, "We could make life easy for both of you in the Republic." If that fails, retry #1 through #6 in order until it works. It should work by the third time. You'll get no exp but will get the passcode needed to enter the Sith Base at Ahto East.
Not all those who wander are lost.-J.R.R. Tolkien
I believe in Christianity as I believe the sun has risen, not only because I see it but by it I see everything else - C.S. Lewis