Hi, I have an iMac and would like to be able to play to a pair of Mackie MR8 Mk2's (http://www.kraftmusic.com/mackie-mr8mk2-monitor-speaker-studio-essentials-bundle.html) and a 12-inch powered Sub (http://www.amazon.com/Polk-Audio-12-Inch-Powered-Subwoofer/dp/B000092TT0/ref=cm_cr_pr_product_top). What's the best way to be able to play from my iMac to both? I'm guessing I would need some sort of mixer/amp. What would be the best and most cost effective way to do this? Thanks for the help.