When I was at the Fort last month, I watched the fireworks from the beach.
Some fireworks are shot low and are directly over the MK. These are partially obscurred by the trees on Discovery Island. But most fireworks are shot way up high and a little more to the right (like it's over the back of the swamp behind Fantasyland) which are fully visible. The audio is piped in as the PP said.
An alternative we've done is to take the boat over to the Contemporary and watch the fireworks from the patio on the main concourse level (I think it's level 4). Go inside the CR and up the escalators like you are headed to Chef Mickey's and the concourse shops. On the end of the councourse nearest BLT, go out the door like you are taking the elevated walkway to BLT and there are some benches there facing the MK (also with music piped in).
This, though, is a popular option so you need to be there about an hour in advance if you want to snag a bench. We got there about 15 minutes before so we climbed the external stair wells on the inside/underside of the concourse rooms and watched it from there. We were essentially two floors above the patio directly above the monorail line coming from the MK station. We could see and hear well from there as well.
Seeing the Fireworks from the beach of the Fort Wilderness Resort is just one of the great many benefits that sets the Fort apart from other RV Resorts. Sometimes the mosquitos will each you alive and every now and then their is no sound track, but who cares that view is still fabulous!
Get a pizza from trails end to go, snag a seat on the beach, enjoy! They haven't always piped in the music I don't believe but they have in recent years. It's so relaxing and exciting at the same time.