Trouble with computer output to monitor speakers via RX2

I'm having issues trying to get a clear audio signal to my Yamaha HS5's. I have my macbook pro connected via USB to my XDJ-RX2, which has the master outputs to my HS5's. 

Playing tracks in Rekordbox export mode works just fine, but when I try to play any audio from soundcloud/beatport on macbook pro (using Rekordbox Aggregate Device audio option), it sounds like it's echoing/spiraling and I have to switch the audio immediately.

I've tried adjusting the aggregate device settings in the Audio MIDI Setup, but I still couldn't figure out. At one point my macbook crashed in the process as well.

What am I do doing wrong? And how can I get a solid signal from my macbook into my monitor speakers via the RX2?

Thanks in advance for your help