If you're interested in the sound synthesis capabilities of the Apple IIGS, you should skip the emulators and go straight to the real thing if you can. It appears that most emulators don't do a good job of emulating the Ensoniq chip. Check out this demonstration of a few emulators compared to a real IIGS:

https://www.youtube.com/watch?v=Y10Wn0JVnXk