Quicktime 5 and later can load and use soundfonts.

For MacOS put the soundfont files (.sf2) into the
Extensions "Quicktime Extensions" "Sound Banks" folder
and open the "Quicktime Settings" control panel and choose the music item
and the soundfont files should appear in a list along with the regular
Quicktime synth.

For MacOSX put the soundfont files (.sf2) into ~/Library/Audio/Sounds/Banks.
Open the "System Preferences", select "QuickTime" and "Music",
and select the SoundFont name from the list and click "Make Default".