It looks like you are using an ad blocker. That's okay. Who doesn't? But without advertising revenue, we can't keep making this site awesome. Click the link below for instructions on disabling adblock.
Audio Interface. You need to be able to send the audio from your computer into both the sub and the monitors at the same time. The best one for the cheapest price is the Apogee duet 2.
Your interface will also allow you to record with a microphone into your DAW.
This is all very important shit. if you acquire this stuff your mixes will improve wayyyyy more and you will be able to further pursue that "pro" sound you want.