This will work with any version of SRB2.
To start, we need a SoundFont (SF2), like this: Link
A good place to find SF2s is this website: Musical Artifacts
METHOD 1: After downloading your SF2, Copy/Paste it into the folder that you installed SRB2 in, open up SRB2, open the menu, go to Options, Sound Options, turn MIDI Music ON (if it isn't already), change the Music Preference to MIDI, go to Advanced Options..., change the MIDI Player to FluidSynth, then go to the FluidSynth Sound Font File box and type the filename of the SF2 you chose.
METHOD 2: Download VirtualMIDISynth and MIDIMapper. After installing, open VirtualMIDISynth and click the plus sign to add an SF2 to the list after finding it on your PC. Once you do this, go to the MIDI Mapper tab and change the Default MIDI Out device to VirtualMIDISynth #1. After you do that, you can change settings to your liking in the Options tab or simply click Ok. Then you have to turn MIDI Music on in SRB2 as explained in the previous method, but don't change the MIDI Player to FluidSynth or type the SF2 filename in Advanced Options. Instead, change it to Native.
Hopefully this helps someone.
To start, we need a SoundFont (SF2), like this: Link
A good place to find SF2s is this website: Musical Artifacts
METHOD 1: After downloading your SF2, Copy/Paste it into the folder that you installed SRB2 in, open up SRB2, open the menu, go to Options, Sound Options, turn MIDI Music ON (if it isn't already), change the Music Preference to MIDI, go to Advanced Options..., change the MIDI Player to FluidSynth, then go to the FluidSynth Sound Font File box and type the filename of the SF2 you chose.
METHOD 2: Download VirtualMIDISynth and MIDIMapper. After installing, open VirtualMIDISynth and click the plus sign to add an SF2 to the list after finding it on your PC. Once you do this, go to the MIDI Mapper tab and change the Default MIDI Out device to VirtualMIDISynth #1. After you do that, you can change settings to your liking in the Options tab or simply click Ok. Then you have to turn MIDI Music on in SRB2 as explained in the previous method, but don't change the MIDI Player to FluidSynth or type the SF2 filename in Advanced Options. Instead, change it to Native.
Hopefully this helps someone.