GoG really needs to start adding a BASSMIDI/OMNIMIDI and soundfont package to their DOSBox offerings. The soundblaster/GS Wavetable synth's sound like garbage in old games and there's really no reason for it. Also, many dosbox games are missing the install option to setup the sound to use anything else besides their default which is worse sounding than than the original soundblaster midi synths I suspect they're using the GS wavetable through the emulator.

This is similar but not a 100% match:
https://www.gog.com/wishlist/site/better_music_quality_of_formerold_dos_games

They are using the game files as they were and the music options are the same as in the past. The wavetable synth has to do with the windows driver of each user not with a GOG choosing about how the sound has to work.

For better sound the solution is the install of third party sound emulators, soundfont based emus like VirtualmidiSynt, Bassmidi or Fluidsynth or emulators like Munt.

Does this also affect the sound effects themselves? The sounds in my GOG U5 are not what I heard from the original game back in the day.

Indeed, it's sad GOG sells these games with rather lame sound configuration. I've enhanced all of them with the Ultima-Patcher and/or by using Taewoongs old Custom-Dosbox and the Roland-ROMs. Everything is in one folder now, without the need for external programs like Bassmidi or Munt. And it sounds absolutely beautiful.

edit: the newest Dosbox ECE has the ability to use soundfonts without the need of external programs as well. I tried some games with the free sgm-v2.01-soundfont (a very well balanced one in my opinion). Works perfectly. I still prefer the simpler MT32-emulation-method for the Ultima games though.

Emulators like Bassmidi or Munt have effect in the music. The U5 DOS version lacked music, but can be added general midi with a patch. In this case the midi sound played under the default windows synth can sound pretty bad, and that is the reason bassmidi or virtualmidisynth should be needed.

In any case any emu or patch is responsibility of each user, because every user has different preferences and different computer configurations

Exactly. That's why I prefer clean and nifty "boxed"-solutions via Dosbox ECE. I never had any problems anymore on different computers.

DOSBOX ECE has Munt Bundled and much more. But the user needs external Roland propietary ROMS for the proper functioning and that ROMS are not free or open source. So is responsibility of every user choosing what they want to do or install, not GOG.

Yes, the Roland-ROMs are not open source (I guess that's one reason why GOG won't be able to bring us glorious MT32-music in their games - it would be a legal nightmare to get the rights to use the ROMs in their emulation). But Dosbox ECE supports the use of free MIDI-soundfonts as well. In the end it's always the user's decision, sure. It's nonetheless sad that GOG isn't able to sell these classics in their optimal sound configuration.