CDJ3000 Control Mode Rekordbox (Windows) Settings

Hello, I'm trying to use CDJ3000s in Control Mode with Rekordbox (Windows) but the Audio and Output PREFERENCES only let me Output one CDJ.....I.e. one channel. I cannot seem to have both CDJs output. I have v6 of Rekordbox. At least by just linking the two CDJ3000s via USB to my laptop I can control the tracks and ONE channel thru the mixer. But not two channels. I saw Mac has an aggregator that aggregates the two CDJs.... I believe Windows automatically does that too. Because in PREFERENCES it gives me selection options of 2-CDJ-3000 AUDIO and just CDJ-3000 AUDIO. The PREFERENCES that I am using are AUDIO "Speakers (2-CDJ-3000 AUDIO)" and my OUTPUT Deck 1 is also "Speakers (2-CDJ-3000 AUDIO)" but then it won't let me also add OUTPUT Deck 2 as "Speakers (2-CDJ-3000 AUDIO)" without deleting the selection in Deck 1. What am I missing here? Many thanks. ***As a side note, I've also tried linking a third USB from my DJM900nxs2 to my laptop, but it gets even more complex. But if the solution involves this third USB link from Windows Laptop to the DJM900, please let me know.