Thanks for your reply sour_grapes, I've not done a kit before. I understand what you're getting at, use the natural juices for the best final product. Unfortunately, I have only 2.5 gals of backyard boysenberries and the 96 oz of currant concentrate. To make 5 gals I'll need to add both water and sugar.
Since my berries are frozen, I'll heat a gallon of water and squish 'em good. I'll try to break open every berry and release all the juices. This will cool the water down and thaw the berries so I can add the currant concentrate. I'll be using a mesh fruit bag. The recipe for the concentrate says I'll need approx 12 lbs of granulated sugar to be added to make 5 gals, so I'll need to dissolve some sugar in a couple gals of water and add to the mix. I'll do this a bit at a time and measure SG to be sure I end up at a starting SG of 1.09ish. I'll guess I'll need less sugar than the recipe says since there is sugar in the boysenberries.
Boysenberries can also be tart, even when fully ripe. They may contain enough acid to allow me to not add any, or not. Once my SG is good I'll measure acid and if it's over .55 I'll leave it. If it's lower I'll add acid to bring it to .55.
I understand that wine from concentrates can be bottled earlier than wine from fruit. I'll probably rack a couple/three times and use a clarifier. Maybe 90-120 days after fermentation I could bottle, if clear.
Thanks again for your reply, I appreciate any and all information!