In the outdoor courtyard area in front of Gasparilla's (near the marina). You can hear the music from this location. You can also watch from the boat dock but the music is not piped in there.
As Tuvalu said, the court yard plays music. However, it's not my favorite view, I would definitely suggest walking past the GF Villas and wedding pavilion to the smaller beach by Polynesian, though you cannot hear the music. It's never been crowded for us and the view is magical
The end of the boat dock is one of the best places on property to watch the fireworks from. There are a few moments in the show when fireworks will fill up your entire field of view.
There aren't speakers out there, but you'll still be able to hear the music echoing from various sources around the lake.
Get there early if you want a space on a bench.