Dairy cake= a ready made mix.
I was discussing this with my sister a few months ago, and our goats are fed so much better now than they were 30 years ago. We use ready made sheep/goat mixes (plus we do use a cattle mix occasionally for copper and we use cattle dairy nuts) whereas 30 years ago, you couldn't buy those types of mixes. You could only get a few straights, and pony nuts. We used to feed pony nuts, wheat, oats, chaff, beetpulp- and we couldn't get soya then to add protein either. As Jane says, its the minerals that are hard to get right if you mix your own. Its also difficult to mix food for just 2 goats- you might have to buy a ton of barley, a ton of maize, a ton of linseed flake, a ton of soya- thats 4 tons of feed that you have to keep somewhere just so you can mix it up!
What I might be tempted to do in your position- is ask the people who have the stud male, if you could buy from them. Or offer to put in money to help buy the straight foods for them, and then in return get bags of feeding for your two.
Beth