Better SoundFont overriding with substitution of missing sounds

[KirbyJoe]

Is your feature request related to a problem? Please describe.
When you use multiple SoundFonts to add missing sounds, some of the sounds in the instruments will still appear to be missing. This is especially common for SoundFonts with missing percussion sounds. I have multiple SoundFonts and change them by mood, but when I use the ones with missing percussion sounds, I always find it incomplete. It appears that OmniMIDI overrides each instrument, but doesn't override the sounds of each instrument individually.

Describe the solution you'd like
Implement a new method of SoundFont overriding that overrides the sounds of each instrument individually. The current override method should be used when there isn't a single missing sound in an instrument. The new method shouldn't directly edit a SoundFont and shouldn't be memory or CPU intensive.