I've used split pig trotters for the same reason. Super cheap way to bump up callogen.
Rick, try a round without roasting. I do the initial first run, strain and then add more water for reremoulage.
I use simple mire poix with garlic, tomato paste and any tomato scraps we might have. Obviously strain through chinois every time you switch vessels.
When the first and second runs are done I combine them and reduce. At this point the stock only becomes a dark brown. I take a crap ton of a soft, not so tannic red wine and reduce that through barely a summer. The surface never breaks a bubble. This gets done in a stainless steel pot. It's important this part happens very slowly to prevent bitterness. If the flames crawl up the sides of the pot it will burn the edges inside the pot, making the wine bitter. If the wine boils, the volatile "fruit" characters disappear.
I take 2 gallons of red wine and reduce it to 3 cups (ish). It varies with the types of wine used. I buy a lot of malbec box wine for this but sometimes I'll get the "expired" bottles from the bar. I never use "the good stuff" wine when cooking. Once it hits the heat all that goodness is gone. I save good wine for its intended purpose- drinking.
But I digress. Once that wine has reduced, and once that veal stock has come close to desired consistency, I strain (crucial step) the red wine into the freshly strained "demi". I add about 15 crushed raw garlic cloves, sadly to taste and stir this in with 2-3 sprigs rosemary. Drop the rosemary in and allow to steep/simmer for 5 minutes then strain.
This is the demi that we use as our steak sauce, and it's also a great springboard to add other flavorings. I even finish Bolognese with it. The sauce isn't bitter, it's meaty and somewhat sweet.
Rick,I know you know all this above, but my point was give your glace a shot without roasting. I believe you'll notice a marked difference in volume with your finished product.
Oh, I forgot a step. Before starting your stock it's good to blanch the bones. If they're frozen this id's even better. I just throw them in a pot and cover them with cold water to 3 inches above the bones. Put on med high heat and once it barley starts to boil I shut it off and strain. I then thoroughly rinse Each Bone. This is paramount to making a clean, bitter free stock/glace.
This is just my 2 cents
