This is a work-around for those who could not setup the game for using a General MIDI device as intended.
(I run a few circles around the sound setup until I realized what the problem was. It is not the fault of the sound drivers but the wrong value(s) written in "sound.cfg". I think it could be permanently solved by debugging "sound.exe" or "dlsnd.exe" but this is way above my skills. I simply wanted to have a dual sound card setup with an SB Pro II compatible card at 200 / 7 / 1 and a real MPU 401+SC-55 at 300h, not 330h. It did not work right away.)

In both the original CD version of the game and the later, JEWEL case version there is a bug which can abort the game's start-up with an "invalid driver ID" message
if you selected "Generic GM" sound drivers. Strange it is, a comment says in "sound.ini" that this "Generic MIDI" ID issue is solved since v2.0. It is not.
Mind you, both versions of Dark Legions CDROM have their own patches to step up from v1.0 to v1.1, which means that the game will use AIL32 drivers (*.dll files instead of the old *.drv files) but the "Generic GM" problem persists.

Running "dlsnd.exe" and selecting option B: "Generic GM" for music is basically the same as selecting option A: "Sound Canvas".
This can be observed in the file "sound.ini" which governs the selections made by "sound.exe" (Dark Legions v1.0) or dlsnd.exe (Dark Legions v1.1)
as the sound drivers will be the same: mt32mpu.adv (DL v1.0) or a32mt32.dll (DL v1.1)

"Generic GM" however, never worked for me.
I found that it is better to avoid selecting "Generic GM" , using "Sound Canvas" instead.
The only difference (aside from the "driver ID") between the "Sound Canvas" and "Generic GM" menu items is that selectable resources are not the same,
for example port address 300H is not offered for a "Sound Canvas".

If you have your MPU-401 at an unavailable address, this can be amended by editing this section in "sound.ini".
For example, you have a GM device at 300h. (The IRQ you select will not be used, just do not select the same IRQ as that of the digital sound card.)

[StartRecord]
[CardName] [Roland SoundCanvas]
[CardId] 120
[CardGroup] 4

[MidiDriverName] [a32mt32.dll]
[DigitalDriverName] []

[MidiDriverChunkNumber] 2
[DigitalDriverChunkNumber] 2

[NumberOfMidiAddresses] 4
[MidiAddress] 0x330
[MidiAltAddress] 0x332
[MidiAltAddress] 0x334
[MidiAltAddress] 0x336

the above section must be changed to:

[NumberOfMidiAddresses] 5
[MidiAddress] 0x300
[MidiAltAddress] 0x330
[MidiAltAddress] 0x332
[MidiAltAddress] 0x334
[MidiAltAddress] 0x336

That's it, I hope it will prove useful for others in the same boat with this game.