Bob each favorite button has 10 preset sounds and yes the volume is adjustable. The easiest way to understand how it works is that Fav1 and Fav2 has their own buttons and all you do is simply push the desired Favorite button and it pops up those 10 sounds. To go back to the main library simply push the Favorite button again and your right back where you was on the main library. Super super easy.
To select a sound to favorites simply go to the desired sound, press and hold and after a few seconds its set. To remove simply do the same. The long press and hold locks it in or takes it out of the favorites.