For personal reasons I won't purchase alcohol or have it in my home, but I'm a bit of a foodie and love Chicken and Steak Marsala.  I've found decent nonalcoholic substitutes for dry and sweet white wines and burgundy (Meiers Sparkling Juice), which covers most of the recipes I've wanted to make, but I've never found a good substitute for Marsala.  Are there any non-alcoholic versions that would pass in a recipe, or a decent mix of other juices or ingredients that would pass, even if I have to process it somehow? 
It's very difficult to replace Marsala - it has plenty of flavors.  There is a fair chance that you like a specific flavor within the Marsala, which is the important distinction you desire.  The flavors of Marsala are often describes as walnut, curry plant (Helichrysum italicum - not to be confused with curry leaves), chocolate, leather, honey and dates, together with a distinct acidity and saltiness.  So, if you want to recreate the flavor, you have to experiment with these flavors, instead of "doing something with grapes". The most difficult part of course is leather.  I would try long-brewed green tea, which will end up with a lot of tannin - this is the bitterness and astringency you need. Together with dark chocolate, honey, salt and wine vinegar for the acidity, you could, in theory, create something similar.  If you want to cheat, you can just get Marsala flavoring, f.e.: http://www.bickfordflavors.com/products/marsala-flavor 