Okay, let's rewind a bit...
First, how are you outputting the video from your computer to the SVM? It's not exactly designed for use with rekordbox and is best suited to mix multiple sources of video together, whereas rekordbox mixes video within the software.
Second, what are the devices you're aggregating for the master and headphone output? An aggregated audio device is when you have more than one audio device that will send output, but in this situation, you're using the SVM; a mixer with headphone monitoring itself. Your audio preferences, regardless of which audio device you're choosing, should be used in external mixer mode. That allows you do assign the outputs of each channel from the software to the individual audio devices of the aggregate, which would then send their outputs to the mixer. Plug your headphones into the mixer, cue the channels as needed.