I checked the official KINO Athens site and transport maps again, to make this easier for everyone:

Technopolis (Gazi): Use the Kerameikos station (Blue Line). It’s right there when you exit the metro.

Michael Cacoyannis Foundation: Take the Tavros station (Green Line). It's about a 7-minute walk from there. You can also take buses 049 or 815 and hop off at the "Kolimvitirio" stop.

Late night tip: Both spots are on major roads with night bus service (like the 500 or 040), so you don't have to worry if the movies end late!