Subte A sounds d . I prefer buses though . Check omnilineas.com.ar what bus leaves you closest.
A word of advice re security. If you are fairly new to BA and not only new to the forum go during the day . Koreatown does have a reputation and some of it deserved and almost none of it to do with the Korean residents.
I go almost everywhere but when people tell me it is unsafe I take precautions in the sense that I know my routes by heart so I do not need to look like a foreigner ,so I can walk at a good clip signalling to get out of my way etc.
Any barrio is unsafe where you make yourself look like a target.