from Amalfi, you can take a bus up to Ravello - well worth a visit. Take a bus or boat back to Salerno and bullet train "Frecce" back to Rome.
Bullet train doesn't go to Sorrento - get off at Naples and take the Circumvesuviana train to Pompei or Sorrento
For a one day trip, I'd do either Pompei + Sorrento (or Naples) or Amalfi +Ravello (via Salerno)