Mac Catalina sound

Need a bit more info... are you using the DDJ-400 as your default output? Or are you trying to adjust the volume of the DDJ using the Mac volume controls? Which application are you in at the time?

are you using the DDJ-400 as your default output?  yes rekordbox aggregate device

Or are you trying to adjust the volume of the DDJ using the Mac volume controls : no

Which application are you in at the time? I unplug the console's usb and I can no longer adjust the mac volume with the F11 and F12 keys. ... the audio does not change and does not come up internal speaker

sorry for the translation ... I am Italian.. 

Sorry - I'm asking if the DDJ-400 is the Mac's default output (or the aggregate) for system audio. That would be why - there is no software volume control for that. You should change that by holding the OPTION key while clicking the speaker icon in the menu bar:

Change your Output Device to be Internal Speakers.

ok .. thanks ... if I create a second user account ... without changing the audio configuration all the times, does the recordbox license work on both users?