You still can't plug composite/stereo cables into a Coregrafx, which didn't even exist at the time. The PCE equivalent is the mismatched AV Booster, which aside from the difference in color, turns your PCE into a diving board.
Most kids in Japan (sitting in front of a TV) probably turned it sideways to use it. Where as TG-16 players probably just stacked it in with their entertainment centre.