Which format are you using the sounds (WAV, Ogg Vorbis, MP3)? Using WAV is preferable for short, repeated sound effects as it uses less CPU to decode and has higher quality (since it doesn't use lossy compression).
I checked to see how many channels the master bus has, and it godot told me 1. Is the channels how many voices it has for the sound card?
No, Godot can play as many simultaneous sounds as your CPU can handle.