Everybody knows that Quicktime built in synthesizer isn't very good, even with the original Roland based QuickTime Instruments.
This synth can be improved in several ways. The easy way is with a better sound set, in the form of SoundFont bank, as it can load it and act as SoundFont player.
The picture is self explanatory:
We can see a folder inside the QuickTIme folder named "Sound Banks", and the new added sound bank "Pro Audio" (.sf2) file selected in the QuickTime preferences.
Notice the increment on Mac OS system RAM usage accordingly to the size of the SoundFont Bank file.