Intriguing question about the Istari. Who knows, maybe Gandalf and Saruman had a singing contest before Gandalf was imprisoned on Orthanc, instead of the Jedi-style duel we see in PJ's movie? Or their staves may have doubled as woodwind instruments, as suggested
here - although I'd rather think of them as something like didgeridoos (which I've heard can have powerful magical effects if played by an initiate) than counterbassoons.
Seriously - what's the deal with music and magic? Given that Ea and what we would call the laws of nature governing it were created by music, it seems quite natural that they were also most easily influenced, bent or changed by music. Which makes it all the more puzzling that on the few occasions where we see the Istari working obvious 'magic' (e.g. Gandalf when the Fellowship was attacked by wargs in the foothills of Caradhras), they seem to have used spoken spells rather than songs - after all, they were Ainur who had played their part in the Great Music, so music would have been their native tongue, so to speak. The only explanation for their apparent abstinence from singing that I can think of is that it was part of the restrictions the Valar imposed on them - that they were actually forbidden to use the kind of power that would have come most naturally to them and had to make do with mere spoken words instead.
(For previous discussion of the matter, see
this thread.)