I installed a VM and it seems like some of the issues were coming from the GOG installation, to both the GOG game and the DVD game. First the SW mode scaling issue was gone so I could handle it correctly with DxWnd. Next the GOG game stopped crashing.

The first red flag was seeing the GOG executable setting the classic window style. They were compatibility setting and then deleting them with DxWnd's setting, both games were consistently starting up. GOG has an advantage here: its newer executable (does anybody know about Gulfino's patch?) is better compatible with DxWnd's blitting techniques, so I could fullscreen it directly. The videos scale correctly and the Captions are visible.

The DVD version has a lot more problems. Although both games are running on ffdshow, maybe ffdshow installation uses a different renderer than what the newer GOG executable mentions (probably something like VMR9?). I can force it to use Overlay which works better. Then it also doesn't show the captions unless a video stops and trying to fix it again degrades video rendering.

MIDI is another issue: Coolsoft MIDI Mapper should do it

Also certain graphical issues on my Nvidia, and DDrawCompat is more tolerable of the video than dgVoodoo2

Talk about 'good timing' or when something is 'meant to be'... Paid off my credit card and have a fresh new statement for the month and boom - a vintage 12x DVD drive pops up on eBay from 2000 for as little as £13. It is made by a brand called Delta, which I can't say I've heard of though.