It really comes down to price I think. Mine get dairy nuts and oats (because its cheaper and they are milking), it's higher protein than normal goat mix. But for example my GG's do not like the dairy nuts as much (love the oats), because they were fed on A&P all round goat mix at their first home. I still buy a couple of bags every three weeks or so to keep them happy, and once they are dry they will go back onto it completely (at maintenance quantities as well = only a handful a day). But GG's do better at a lower protein level than other breeds.
I would also say that with a lick available the sheep mix is ok too, especially if they like it, have been used to it at their previous place, and if you are only feeding two it may just be unecnomical to have loads of different types of food around. and you are probably getting a better price per Kg if buying from a local farmer, A&P is about 13 quid for 20kg, C&B dairy nuts is around 7.50 here for 25kgs.
However sugarbeet shreds are good (I feed them to my sheep in the winter too, only the girls though), and they can have them dry (if they like them). Good to feed soaked in HOT water in winter as a mid-day warmer.