Angel De Brito and Laura Fernández just announced a new twist for the following round called "THE CHALLENGE":
Couples will have to pick between 30 envelopes containing 30 different songs from different rhythms, languages and decades. They have two chances: if they don't like their first choice, they can opt by another one. However, this decision can't be changed and they must stick with it.
Also there's a Wildcard that allows one couple to choose their song.