To record with Serato DJ Pro and the XONE:DB2 and XONE:DB4 mixers you will need to set up the mixer for recording. You will need to designate a channel to use for recording and then select this channel in the REC panel in Serato DJ. This will record the software mix. You will not be able to use this channel for Serato DJ Pro while it is used for recording.
Designating a channel is done from the XONE:DB2 and XONE:DB4 hardware using the Menu button and Display Screen. Navigate to ‘USB Routing’ and selecting ‘Record’ on the channel you want to use. You must then make sure Serato DJ Pro is recording this nominated channel in the REC panel.
You can find out more about Routing and these menu features in the individual hardware User guide.
The XONE:43C also requires that you designate a channel for recording, however this is done in the REC panel in Serato DJ, and does not need to be done on the mixer itself.
Once you've selected your desired channel, connect an RCA cable from the REC OUT port on the back of the mixer, to the INPUT of your aforementioned, desired channel.
You can read more about recording in Serato DJ Pro in our How to record and share your mix with Serato DJ Pro guide.