I am interested in knowing how I can increase the solubility of gelatin, marrow, and minerals in my stock.
Thanks.
Meat – How to increase the extraction of gelatin and minerals from bones into the stock
bonesmeatstock
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This is going to be tough to answer. Too many variables.
I pressure cook all my saved chicken bones until they can be pulverized easily between two fingers (only about 1 hour). Then I reduce the stock from 3 quarts down to about one. When cooled and poured into a can-and-freeze jar it will typically gel at room temperature.
The answer depends highly on the amount of feet used, the amount of water it was cooked in and how much reduction is preformed.
Marrow bones add a marrow-y flavor. That flavor is very thick and rich, but can taste of innards. Have you ever eaten marrow? (It's delicious, as far as I'm concerned. You can roast and add a touch of salt if you want.) I would say that it sounds like you've got a lot of marrow bones in your stock. That could cause problems, since even a few marrow bones will make the stock fairly greasy. Marrow is almost all fat.
The ox tails have lots of bones in them. They'll give you the deep flavor and gelatin of bones. (Neck bones give you the same thing, as you can see from the picture below.) The only thing marbled meat would have added is extra fat, which isn't necessary for stock -- you'll end up skimming the fat off anyway. You want both the bones and the meat for stock, as you would for chicken stock. It's true that marrow bones are fairly clean, but they're used for a different flavor.
Another option for adding lots of flavor is to add what are known as flanken style ribs. This is short ribs that are cut across the bone. They're also used in Korean Short Ribs. They give you some of that marbled meaty flavor, along with the bones from the ribs. 
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Best Answer
In terms of commercial food processing, there are more efficient ways to extract gelatin than slow-simmering the bones, generally by treating the organic matter with a strong acid prior to boiling, then using commercial evaporation and filtering equipment which is far more efficient than anything a home or even restaurant cook has access to.
According to Gelatin Food Science (see the "Gelatin Manufacture" section) it can also be first treated with a strong base solution before acidifying it, which lowers the isoionic point. It's kind of difficult to explain exactly what that is if you don't have a background in organic chemistry; technically speaking it's a relationship between pH and electrical charge - but applied to extraction it refers to the pH at which the solubility of a protein (such as gelatin) is the lowest. Lowering this is a good thing in extraction, because it means that the gelatin will be easier to filter out in an acidic solution.
Thus I have to point out the question is actually a bit contradictory; if your goal is the extraction of gelatin then you want to decrease the solubility.
But I think this is all going to be beside the point anyway, because none of this applies to stock making; the goal in food processing is to extract the pure gelatin, not to get a flavourful stock. When making a stock you definitely don't want to use an acid solution, it's going to ruin the flavour.
Realistically, when it comes to stock-making, especially at home, the only way you're going to be able to extract more gelatin is to simmer it longer. That's it. When the bones break without any resistance, that means you've denatured all the collagen and you've got all the gelatin you're going to get. I wouldn't worry about solubility because typically in stock-making you're already using more than enough water to dissolve all the gelatin that you could possibly hope to extract.