I periodically substitute various forms of alcohol in certain dishes for friends who (for religious or personal reasons) choose not to have any kind of alcohol in their systems. (Ha! I also substitute bacon for my Jewish and Islamic friends. THAT gets interesting. Esp if they keep kosher)
The taste will always be somewhat different, and sometimes it's better to completely work a different angle (for example; tomato paste and beef bouillon instead of red wine for one dish because it's looking for the depth and richness a bold red creates... or a mushroom reduction with another... or plum and cherries on another. None of this helps you, btw., because those are red wine fixes... excpet that the mushrooms which be red or white substitution depending on which variety of mushroom is used. But marsala is AMBER. It's more like a liquor).
There is no "quick fix" for all kinds of alcohol. White grape and white wine vinegar can work for some white wine recipes but not all. What I do is look at what the alcohol imparts:
For madeira wine it has a very rich, buttery, nutty flavor with a hint of smoke and a little very subtle tart fruit.
For "virgin" chicken marsala I would use
- bacon fat
- butter
- toasted pecans
- chicken broth (extra on top of what is already called for)
- 2 or 3 drops of liquid smoke
- some (just a few to a small half handful) of dried cherries or cranberries (optional) if you're using thighs....OR....possibly capers. I know. Two radically different things.
I would NOT use vinegar or white grape+vinegar in this dish. Too acidic. You're looking for a round/buttery feeling. Purple grape would be WAY off base (like catsup for mustard). Apple would be closest. But I would rather just skip the wine OR the above substitute than use apple, personally.