Błędnie: I'm afraid we're miles away as far as basic assumptions are concerned. An agreement is simply impossible. Poprawnie: I'm afraid we're miles apart as far as basic assumptions are concerned. An agreement is simply impossible.
Idiom "to be miles away" oznacza 'być myślami daleko stąd'. "To be miles apart" oznacza natomiast 'różnić się' (o np. opinii), 'nie zgadzać się', 'być diametralnie odmiennego zdania'.