Your piano wire might be stainless steel or chromed. At any rate, it's not likely you will be able to braze it with a propane torch, you will need a small acetylene rig.
Check out tinmantech.com for some supplies you might need. Kent White (who runs Tin Man Tech) is a master fabricator like they don't make anymore, someone for which the word master was invented....
I think he may have some silver braze that might work. Check out the Meco small torch as well, I use it for everything.
(not a master, still lots to learn)