Hi Franco,
Glad you figured out that you needed "Hide resting staves" - I misunderstood you to mean just certain measures
For Cantabile, you should be able to use a virtual MIDI cable to send your signal from Composer to Cantabile. So really all you need to do is install something like the LoopBe cable (or you can purchase LoopBe30 if you need more than one cable/16 channels). In that case, you will not need to get SynthFont.
ttfn,
Sherry