I think vdmsound project was the answer to these sound / speech problems. Sadly the project has been inactive for some time. Like 5 or 6 years. I believe the project is/was open source .. (licensed under GPLv2). Would be great to see it reactivated. Perhaps some kind of new combination project is in order? DosBox, ScummVM, Munt, VDMSound and so on.

Some good info on sound in old games and old hardware.
http://www.vogons.org/viewtopic.php?f=46&t=24769&p=186881&hilit=DDMA%2C+Southbridge%2C+PCI%2C+ISA#p186881

VDMSound ..
https://sourceforge.net/projects/vdmsound/

Demo on YT
https://www.youtube.com/watch?v=jcb5PBt5YgY

Guide to VDMSound ..
http://www.vogons.org/viewtopic.php?t=2389

From the readme file ...

" VDMSound is a program that overcomes what has probably been the most exasperating limitation of DOS boxes since Windows NT - sound support. VDMSound is an open, plug-in oriented platform that emulates an MPU-401 interface (for outputting high-quality MIDI music), a SoundBlaster compatible (SB16, SBPro 2, SB2, SBPro, etc.) implementation (for digital sound effects and FM/AdLib music), as well as a standard game-port interface (for playing games with joystick support). In development are improvements to the existing joystick emulation, and possibly VESA support.

Unlike all the Win9x SoundBlaster ISA ‘legacy’ drivers available from a variety of PCI soundcard manufacturers, VDMSound is not a mere ‘wrapper’ or ‘bridge’ to existing audio hardware. It is a self-contained, 100% software emulation program that is completely independent of your audio hardware type and settings. VDMSound works with any soundcard, and will even work on computers that have no audio hardware at all (for instance, instead of outputting sounds through your soundcard using the standard Windows drivers, VDMSound can easily output them to disk). "

---

Edit: update ..

I think it has a lot to do with old DMA / DDMA verses modern hardware, like PCI. I had some success
with vdmsound on Win_XP. An old 386 / 496 would be ideal. The VDMSound project that is no longer
active. IMHO .. Vlad Romascanu's project was the way to go. Perhaps some kind of combination project
would solve the problem? (VDMSound, DosBox, Munt, ScummVM .. etc.)

==

In DosBox - Microprose SS2 (others)

Sound and music worked, but speech / voices do not. They are like buzzing sounds.

The game is usually started with a batch file named - SILENT.BAT.
Contents of my SILENT.BAT file -- SS2 VGA ADLIB HARDC

I get Music and sound effects from the sub, but no decent digitized sounds (voices).

Music and game sounds are fine via the Adlib selection, but voices / speech won't work properly
at the same time. There is no way to fix this that I know of.

Any solution to this yet?

Silent Service 2
I don't own the GOG version, but I do have an old CD edition of the game.
Also had these sound problems when trying to run the game in DOSBox.
I think the GOG version also supports Roland, it requires the RSOUND.SS file from Game.

Because the best solution is unfortunately to use Roland MT-32.
https://www.gogdb.org/manifest/a6970d4a29d8cb831c428ec32ca5a5ee

Comparison:
ADLIB: Good music and SFX sound, but the voice output is very quiet and not very good.

Roland MT-32: Very good music output, no SFX, but the voice output is of understandable "quality" and sufficient volume via the PC speaker.

First of all you can forget about DOSBox, it doesn't exist anymore, it hasn't been done for over 2 years.
Use instead:
DOSBox Staging
https://github.com/dosbox-staging/dosbox-staging

Additionally you need the ROLAND MT-32 or CM32L ROM files.
MT32_PCM.ROM, MT32_CONTROL.ROM or
CM32L_CONTROL.ROM, CM32L_PCM.ROM

Settings for dosbox-staging.conf
Edits the default configuration of DOSBox staging and overwrites the dosboxSilentService2.conf provided by GOG for the game.

[mt32]
model = mt32
romdir = ...\Path to the Roland ROM Files
mt32_filter = off

[speaker]
pcspeaker = impulse
pcspeaker_filter = on

I don't know if GOG starts the game directly via dosboxSilentService2_single.conf or via Silent.bat, in one of the two files you have to change the start parameters from Adlib to Roland.
The start command of the GOG version should look like this.
SS2 VGA ADLIB HARDC
Modifies this to:
SS2 VGA ROLAND HARDC

All SS2 Options:
SS2 {DISPLAYTYPE} {SOUNDTYPE} {DRIVETYPE}
DISPLAYTYPE: VGA, EGA, TANDY, CGA
SOUNDTYPE: ADLIB, ROLAND, TANDY, IBM (Speaker)
DRIVETYPE: HARDC, 1.4 (HD Floppy),

Delete all files in the DOSBOX folder of the Silent Service 2 installation of GOG and replace them with the DOSBox Staged Version.

It even contains the installation program (INSTALL.EXE) with which you can install the game on a real retro computer.