Yups... We use crushed Cadbury's Flake. If you're on holiday again in Italy, and in the Lucca area, then find a good shop that sells wines and liqueurs and get some Nardini rum. It'll make your Tiramisu taste magical!
I'd never use Marsala, as that's fundamentally wrong. Marsala is for Zabaglione! Amaretto, yes, that works, but you really want some form of strong, dark rum:)
Marco.