@zing I did it and I followed every step they mention (that's the reason I tried with alsamixer) but I'm having the same result. Anyway the version of this case is 7.1.1 and I am using the current stable 7.2.1. Maybe this has something to do? Is there anyway to download the 7.1.1 recalbox version?
PD: sorry for the "spam". I thought that writing in different languages wasn't considered as spam, my fault @Zing