(same post is in X-wing forum)
Get this sound font working with the imuse midi sound system. I don't really think it's possible though.

http://www.bismutnetwork.com/04CrisisGeneralMidi/Soundfont3.0.php

Note even if you can get it working it may have excruciating load times as the sound font uncompressed is like 1.5 Gigs.

Also note he says he had modifications in those demo recordings: like preset levels compression and volume. They aren't just guaranteed to sound like that but you can listen to the imperial march demo and dream . . .

It should be possible to have dosbox send its general midi output to a software midi synth:

The below works for me:
http://coolsoft.altervista.org/en/virtualmidisynth

Select the checkbox where it sets virtual midi synth as the default windows synthesizer and it should work with the gog-configured xwing and tie dos versions.

If you don't want it to be the default windows synthesizer you can set the midiconfig line in their individual dosbox configuration files to be the number of the device (starts at zero), you can see which is mapped to which in a dosbox cmdline with "mixer /listmidi". The line in the dosbox config should be "midiconfig=1" (or whatever number) in the [midi] section.

If the soundfont is compressed you will need to uncompress it with one of the following tools to work with virtualmidisynth:

http://woolyss.com/chipmusic-soundfonts.php#compressors