There is a viewing area at the Contemporary for anybody who knows it is there. I believe it is on the 4th floor. They pipe the music into that location also. You can also view the fireworks from the TTC, Polynesian and Grand Floridian although all those views are ground level. Once we had to leave early for some reason and watched them from the actual ferry going from MK over to the TTC.
Once we disembarked from the ferry at the TTC just as the MK fireworks were starting. Had a wonderful view, including piped-in music, from just outside the ferry dock, and were in our car leaving the parking lot before the hordes leaving the MK after fireworks reached the TTC. At the GF we've watched from the boat dock, which has the advantage of a view of the Electrical Water Pageant (which frequently comes by just before or just after the fireworks, depending on season & MK schedule), but you can also watch from the GF marina just outside Gasparilla's.
We've watched from the lounge atop BLT too, and the locations above are just as good or better since you have a more straight-on view of the castle whereas BLT is off to the side. And something to consider is that the current show relies heavily on projections on the castle, which are not really visible other than inside the MK, in the Hub or on Main Street.