Looking to buy whole Quake series, but conflicting comments about whether or not sound track works properly or at all. Don't mind doing some legwork if there's a pretty explicit how-to, but I'm not keen on trusting non-GOG files. Is soundtrack even an issue or am I just reading older comments that have since been addressed? Not having all-things-Trent is a dealbreaker.

There is no issues and never be. Lamers customers is only issue... Lakers everywhere, many of them now programmers still stay lamo...

Well, there is something about wrong cue files for Q1 disc images make music tracks cut one second +/- from-to neatr tracks. You can download on PCGW alternative cue, or Use CDMage (gog rename images from bin to .gog files - copy and rename it to bin before cdmage) and create cue from it, or rename .gog to IMG mount it in DT Lite SPTD drive and make MDS+MDF image by Alcohol.
3 variation with differ amount of 3rd party downloading.

Or use what GOG give you as is. If there is ind33d any issues (with cue sheets?) - not the major ones. You probably not notice them.

For WinQuake/GlQuake you must mount cue images manually. For Quake.exe (dos) - before installation and launch must have real/virtual drive. For Dos version it can be whatever letter, for GlQuàke it should be first drive (E:).

Or make wave/ogg tracks by extraction them (WMP ITunes VLC or else). Require few 3rd party downloading (DLL files to play wave/ogg/mp3/.etc files locally). Gog lazy to do this for Q1 while they make it for else (cause Q1 is combination of very differ versions with differ solutions to work them on Win Nt and Win 8+ - they chose easiest DosBox music solution only)(lie about legal issues).

There is never any updates for Q series on GOG.

There is major compatibility issue with Q4 (idtech 4 engine) - require manually tweaking autoexec cfg to make proper graphics (initial is not detect gram size). All I saw command prompts is excessive. There should be 1-2 options to make game see VRAM - all else will work from in game settings.

Same for Q2 - its renders never be properly implemented always work as advert for PowerVR and 3dfx (all renders have unique GFX effects even Software mode, require source-port mods or many autoexec tweak commands).

Look to PCGW article and its links (FAQ/console command URL). Default OpenGL is lowest quality, even after Software.
Also GOG support site.

So there is game old and new issues. None of them come after GOG. Nothing special from 3rd party required. U can do every manual or use few/some pre-compiled solutions.