I only know what settings I used to run MechWarrior4: Mercenaries, it varies per game. Try asking in the forum, the creator (and others) is active there (so DxWnd is actually in very active development with new versions seemingly every other week, it's just a huge project to take on really, not outdated).
sourceforge.net
With that said all I got out of DxWnd was the ability to at least run the game under Win10 as it otherwise crashed when ran without it or with other wrappers like dgVoodoo2, I never got the windowed/fullscreen/resolution stuff working as I wanted but after discussing it with the creator it was the game doing things in a weird non standard manner he couldn't figure out in the end (plus there being different versions of the game, I was using the one re-released by MekTek with some enhancements with Microsoft's permission at the time as a freeware title, but it was later abandoned and it's no longer considered freeware).
Since then I figured out a work around for my version which lets the game work without DxWnd and running it with dgVoodoo2 instead now works and it does do what I want with the resolution (still fullscreen though, but at least it works natively and doesn't change my resolution and mess up all of my carefully aligned desktop arrangement). Have you tried it? Its interface is much simpler. Though I had trouble with the latest v2.55.4.1 so I went back to v2.55.4.