Finally solved! Considering that CH seems to be the first place to figure this out, perhaps it's worthwhile to sticky this for any person looking for the same solution. As we've painstakingly found out, there's no comprehensive guide, most recommendations simply do not work. Now we have the solution! So, here it is:
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This may seem like a lot, but it's very easy.
Before starting, you need to download and install 2 programs:
-DosBox
-Timidity++
They're an easy google find. You don't need them running immediately after install.
As well, you need to:
-Have a .mid file on hand for testing
-Make sure your sound card drivers are already completely up to date
Next:
1) Download the driver you think/know has the MIDI Soundfont you desire. If you're unsure, download all drivers you can find for your card.
DO NOT INSTALL ANY OF THE DRIVERS YOU DOWNLOAD.2) Right click on the driver you downloaded and choose, "Extract to XXXX/" (where XXXX is the name of the driver exe file). Do this for each driver you download, being sure to put them all in their own separate folder.
4) Open the folder that the extraction created and use Ctrl-F to find anything called "sf2". There maybe multiple.
5) Move all sf2 files into the "C:\...\...\timidity\Musix" folder or wherever Timidity++ is installed for you. It's fine to rename the soundfonts to anything. Rename any sf2 files that happen to have the same name.
6) In the "Musix" folder, make a copy of, and then open, "timidity.cfg" and erase anything it says, then edit and save to the following:
dir "C:\...\...\Musix" (or whatever the path is to your Musix folder)
soundfont "XXXXX.SF2" (where XXXX is the name of the .sf2 file you want to use)
#extension opt -Od
#extension opt -o0
#extension opt -U
#extension opt -o0
#extension opt -o0 --I struck these out because I don't think you NEED to add them, they should add themselves once you've gotten to step 8. If it doesn't work when you leave it out, try again with them included.
7) In the main Timidity++ folder, open "timw32g.exe".
Open your .mid file in Timidity++ and press play. If this isn't the right soundfont, go back to the timidity.cfg and edit in a new sf2 file name. Once you find the one you want, you can close Timidity++.
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From here, you can do 2 things. Contine to read this, or go watch this video as it shows everything I'm about to say.
http://www.youtube.com/watch?v=fTHwxXpHEeY&feature=player_detailpage#t=66s--You don't need to worry about anything he did before the start time of the video. He was just downloading DosBox and the driver and soundfont he wanted.
9) Open DosBox and type in "mixer /listmidi" without the quotes. A list of all MIDI devices will appear. Take note of what # is next to Timidity++.
10) In Start Menu "Search Programs and Files" type in "regedit" and hit enter.
11) Navigate to:
-[HKEY_CURRENT_USER/Software/Microsoft/ActiveMovie/devenum/{4EFE2452-168A-11D1-BC76-00C04FB9453B}]
--Before continung, export "ActiveMovie" in case something goes wrong.
12) Open "Default MidiOut Device". On the right side of regedit, locate and double-click "MidiOutId". Edit the value to the # that was next to Timidity++ in DosBox.
13) On the left side of regedit, locate "Microsoft GS Wavetable Synth" and locate it's "MidiOutId" on the right side and double-click. Edit the value to one number higher than the highest number that showed up in DosBox.
14) 64-bit users will need to repeat steps 12 and 13 in:
-[HKEY_CURRENT_USER/Software/Microsoft/ActiveMovie/devenum 64-bit/{4EFE2452-168A-11D1-BC76-00C04FB9453B}]
15) Restart your computer.
16) Open your program/software that will play back your MIDI and set the default MIDI device to "Timidity++"
You're done!
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Now any program that plays MIDI back to you should now use the soundfont assoicated with Timidity++ rather than whatever had originally been playing.
I really must extend a thanks to hartbeatmr who spent a lot of time researching this with me. Not many people are willing to really dedicate themselves to others issues, especially not ones that seem so impossible like this one did. Thanks, hartbeatmr!