Hi mld051
Where are your speakers connected to?
You should only have to connect them to the back of your DDJ SB and that should be it. The Focusrite sound card could interfere with it maybe, so give it a go without that connected too.
The best way to get some help with this issue is to hit up our support team by opening a help request here:
support.serato.com
They are best equipped to take a look at the issue and try to find a solution for you, put as much detail as you can into the help request and they will get back in touch with you as soon as they can.
Cheers!
Karl