I played through Wing commander 4 the other day and there are many issues in the game which someone should address. Here are the ones I hit:

1) The DVD version ignores all movie settings. I had subtitles on, didn't see a single subtitle all game.

2) The audio is all wack on the DVD version. The movies I had to put my speakers to 100% to hear them at all, but once I was out of the movies the sound of the game was so loud it could have woken the dead. Someone needs to seriously adjust those two so they are more in synch.

3) The DOS version cannot go past mission 5 due to corrupted music.tre files.

1- the DVD version has no subtitles;

2- that's a codec issue, fortunately I already had X codec pack installed which allows to configure some codecs separately and that solved the issue. There are other methods IIRC including specific configuration tools.

1- the DVD version was still based on the normal version so they left the option in even if it didn't work, keep in mind that updated re-releases of the Wing Commander games were often quite rushed (there's a reason GOG doesn't use the Kilrathi Saga versions of the first three games and went with the DOS releases) and paradoxically the DVD version of WC4 is probably the least problematic;

2- it's a problem with the game assets, every PC has this codec (it's the Ac3 codec) nowadays but the implementation used at the time to encode the movie audio (the DVD version was packaged with an expansion card for DVD viewing back when DVD drives for PCs cost an arm and a leg and DVD playback was too heavy for most PCs of the time, it's part of the reason subs don't work) makes the volume of the cutscenes really low on the stock version of the codec used now, basically it's not something that can be corrected in game files or with a DLL unless they go to the original master files and recode them, you have to get a program that allows to tweak the volume levels for that particular stock codec to compensate.
Someone in the original thread about the problem said a program called AC3filter should allow to tweak the volume levels.
I mentioned the X codec pack because I already had that installed when I first ran the game and it already allow to do that without installing anything else.

2 - Makes sense, but still stinks. As it is I got the DOS version working now, and the volune is just fine there. Still maybe they should consider going in and setting the voulme of the rest of the game softer then, so it doesn't go from can barely hear to rock concert volume. Maybe that can at least be done somewhere in a default setting? Or maybe they could add the codex to the dosbox emulator it uses?

DVD playback in a DOS virtual machine isn't advisable, DOSbox doesn't just simulate software but also the hardware DOS ran on and keep in mind that beefier computers needed specific DVD-decoding hardware (the DVD edition was a pack-in with said hardware) that is not DOS compatible and that DOS video cards simulated under DOSbox probably wouldn't be able to display it properly anyway. You'd probably have to create not just an entire different build of the game but also a version od DOSbox that goes way beyond the scope it was made for.
Besides, ac3filter and similar utilities are easier if you don't need the subtitles (fortunately my english is good enough and once the volume levels were adjusted the audio was clear enough for me).

If you have to make a new build to run the DVD, then how does it run in DosBox in the first place? I still get a message it is running it. Hence my suggestion to add the codex as it appears to already be using it. Either that or they are emulating Windows 95 as that was what the OS was when this was made.

The only issue I had without subtitles is the Kilrathi could not be understood at all due to the faint volume. Thankfully I fixed that by fixing up the DOS version to work properly in the end. Helps I still got my CD's from when I bought the game in 1996.

What are you talking about?
The DVD version doesn't run in DOSbox, it's a windows game that was made later than the CD version.

Well, they are doing SOMETHING, as native win95/98 games refuse to run in Windows 10 usually without some emulation of some sorts, and as the DVD version was released in 1997 (per google) it would have been made for Win95. And seeing as I can get like 5% of native windows95 games running on Win10 without major tinkering or finding a fan patch there's something done to it and the code more than likely somewhere.

I'd check to confirm more but I deinstalled the DVD version by now, since I got the DOS verison up and running.

There is no emulation for windows games, there are usually DLLs that simulate old OS calls or wrappers to interface old versions of DirectX with the newest ones (X-wing vs Tie Fighter uses one of those for example) but they usually don't do anything to mess with the game code themselves. Heck sometimes just the removal of old DRM systems is enough to make some old windows games running.
Usually emulation comes into play only for Glide games and even then it's not exactly full emulation.

What you want is basically going there and make a new windows port of the game, it's way beyond their scope and probably they don't even have the means to do that because often not even the publishers have the source code for their games because they are idiots that treat their games like throwaway trash.

The dll makes sense to me. As for what I want, I'd really like them to fix the DOS version so that we don't have to fix it ourselves, since coding the DVD version to fix those other flaws is probably not going to happen (for reasons like you mentioned too, though it would be nice if as a courtesy they did include the codec you mentioned). That should not be too much to ask. But looking all the posts on it and the fact it's been an issue for 2+ years at least (I didn't go farther back than that) it looks like it is not a priority to them.