I have heard its 35mm optical track, and if the PCM track is anything like that on either the Criterion or Columbia release, it's breathtakingly good.
I'd imagine and hope the 70mm was similar, just discrete. I remember the original DVD having a nice 5.1 track, but the Blu-ray just doesn't feel the same. And honestly, the 35mm presentation I heard blew that Blu-ray away.