I want to share with rw permissions for a selected group of users | chmod g+s /music | setfacl -R -d -m g::rwx -m o::rx /music

Set GID as described above:

Code:

chown -R :media /music
chmod 775 music
chmod g+s /music

ls -ld music should give us

Code:

drwxrwsr-x   3 matty media

*** find a way to set the g+s on all subdirectories ***
This is pretty straight forward using konqueror. Select all the directories and right click, permissions, and advanced permissions. 
From the command line: ???

We can apply acl recursively:

Code:

setfacl -R -d -m g::rwx -m o::rx /music

This creates the default rules for newly created files/dirs within the /music directory and subdirectories. 

If the original files in there were created with a "standard" umask, most of them will have permissions similar to:

Code:

-rw-r--r--
drwx-r-xr-x

Assuming this is the case, we can fix this with

Code:

chmod -R g+w /music