I recently bought a Series III 32SX mixer. I don't fully understand SUBGROUPS. On my current 32.4.2AI mixer I have 4 SUBGROUP faders, one of which I use to control the volume of all the singers. I don't see those SUBGROUP faders on my 32SX. How do I do SUBGROUPS to control a number of singers. Must I create a DCA for that?