I'm supposed to meet a group at Balboni theater on Wednesday but I am not sure where it is. Is it the theater beside the Chosan gift shop?

No, it is next to the White House sort of. If you are coming from the bus terminal, turn left at the drive way just past the parade field and follow it around to the right. Balboni is right there on your right. There is a small AAFES facility over there too.

Is this theater within walking distance from either gate that is near the Samgaki station or the Sinyongsan station? Will I probably have to catch a taxi when I get on post?

I have walked to it from Camp Kim which is no farther than Samgakchi. Just go in gate 1, walk all the way down to the intersection past the food court. Go straight until you are behind the white house. There is a corssover there someplace that will bring you out very close to the theater, I just do not recall exactly where it is. Basically walk straight up the road from gate one until you get past the white house and then head right, it shares a parking lot with the white house, but it is on the side away from gate one... hopefully that makes enough sense to get you there.

Years ago it was THE Theatre on Yongsan. The building next door was the BIG Snack Bar, the present Library was the PX, and there was no Dragon!
Balboni is used for meetings, etc. No regular movies.

I remember the Balboni. I watched the Super Bowl where the Pats won thierfirst one there. If you can get to Noksapyong Station instead, it's closer.

Very true! I was going to suggest that, but I could not remember the gate numbers over there. I think it is gate 7, but I might be wrong. Opposite side of the street from gate 10, and about halfway between gate 10 and the subway station, that is the gate you would take from Noksapyeong.

yes, that would be gate 7

Can someone post all of the subway stations that are near enough to Yongsan to walk to? Also, the directions on how to walk to the base from the station? I prefer to take the subway than the base busses.

Closest one to base is Noksapyeong. It takes a couple of minutes walk to Gate 7 or Gate 8 ( on the other side of the street).You take exit one and go on that road. You will see the gates guards outside.
The base bus I think it should drop you off at Moyer Rec, inside the base, so I would take that if I were you. You wouldn't have to chage so many lines, you know?