I am going to try to explain it to you. I believe that this number refers what the Spanish State gives every year to the King for the expenses of the Headquarters of the State, it is not a money that of to the King but with he has to support the expenses of the Royal Family (in Spain the Royal Family only they are the Kings, the Princes and the Infantas, and they are those who develop official activities),and also the persons who are employed at the House of the King.
I imagine that the King has a personal wealth, with something that he could have inherited and that he has hoarded in the last 30 years, but he cannot be not much less comparable to the wealths of other monarchies. The family of the King lived in the exile for a long time, and when they went away they did not take to themselves almost anything, lived in a humble enough way to be members of the royalty (that enclosed the Queen Victoria Eugenia had to use some of her jewels.)
All the palaces that pertenecian to the monarchy form a part of an institution that is called A National wealth, the Royal Family can enjoy them but they are not of their property. National wealth takes charge of the expenses of the palaces (as the Zarzuela or the House of the Prince), the rest of palaces scarcely are in use (the Real Palace in the big receipts and the palace of el Pardo one like residence of foreign Chiefs of state when they are in Spain), but many of them can be visited as museums