Essentially, the set-up was like this (sorry for the ASCII art):
... for night I:
------------
|synths drums
|
|sax bass
|
|guitar guitar
... for night II:
---------------
| synths drums
|
| sax bass
|
| guitar guitar
[The picture above is from night II.]
As far as these film scores are concerned:
Occasionally, the National Museum of Cinema in Turin commissions new scores by contemporary bands/artists for some of the silent movies from their archive (like Cabira, Rapsodia Satanica, Il Fuoco, The Decay of The House of Usher, The Cabinet of Dr. Caligari, Nosferatu, The Last Command, ...).
Usually, these aren't impromptu performances (as there will have been rehearsals prior to the show). However, these scores do differ somewhat from the regular output of the bands involved. I've attended a couple of these cinematic concerts before and they've always been fun to watch.