Sound/Soundfonts
When using MuseScore2.1, and selecting instruments either in Edit, Instruments or in Staff Properties, Change Instrument there appear to be many more instruments available than when I go to the Program File, MuseScore, Sounds, FluidR#Mono_GM and look at a list of the files in the soundfont. Where do all the other sounds reside or where are they stored?
Comments
Instruments are not Sounds, it is much more.
While MuseScore keeps its default SoundFont General Midi compatible, and is thus rather limited (but interchangeable!) in the sounds it offers; it doesn't stop us from including a lot of definitions of instruments.
An instrument definition contains the transposition it uses, common/professional playable ranges; some hints about how it should interpret some of the articulations and finally also a link to the soundbank it should use for playback.
For most instrument this (by default) uses the "closest matching" thing that is available in the SoundFont.
Adding to the above:
General MIDI indeed defines only a relatively small number of sounds, and nothing MuseScore can do would change that, so most soundfonts will provide only those same hundred or so sounds. The list of sound provided by a soundfont is what you see in the Mixer, and it is usually pretty much the same list no matter which soundfont you load (assuming the soundfont is GM-compatible).
Of course, there are many more instruments in the world than just the hundred or so sounds defined by General MIDI. So MuseScore does try to provide a definition for each instrument, allowing you to write for these instruments and have the correct information regarding the staff name, the default clef, the transposition, the playable range, etc. But when it comes to playback, it's still going to be a matter of choosing one of the General sounds. So for instance, the saxophone family includes over a dozen different instruments, but General MIDI only defines four saxophone sounds - soprano, alto, tenor, and baritone. MuseScore knows the names, clefs, transpositions, and ranges for all the other more obscure saxophones like sopranino or C melody or contrabass, but when it comes to playback these will simply use one of the available General MIDI sounds. So sopranino uses the soprano sound, etc.