By doing a google search I found "GeneralUser GS v1.4.sf2." It contains very much improved presets for all the GM instruments and gives one a lot more, including several pianos, wet and dry, Irish tin whistle, a great cymbals in the melodic pool, several drumsets in the melodic pool, orchestral percussion in the melodic pool (so that on one channel you can have timpani, cymbals, triangle, and all the rest), etc.

It comes with an .exe file which installs it, but I find that the presets can be used as they are, also. The file is about 30MB, but seems comparable to some much larger ones.

Since I can use only one of my hardware synths (Creative sunth A or B), for some reason, but can also use MS GS Wavetable SW synth to get 32 channels, my intention on doing the search was to find a file that would replace the instruments that load with the MS software synth. I haven't got far enough to see if General User v1.4 replaces this as well as the GM bank that loads by default into the hardware synth, but the instrument improvement is worth the price, which is $0.00.

all best,
mgj