Mainstage not working with Trigger and Audio Interface

Hi, im trying to use mainstage for live performance. I am a drummer and will be using some backing tracks using playback. I am also using some wired in ear monitors. Im am running a MacBook Unibody ( not MacBook Pro). Given the lack of funds I currently have, I am not using the best of equipment. I am currently using two presonus audio boxes as an aggregate device. This is so I can seperate the backing track and click in my monitors. I am saving up to get a better interace but for now this has to do. I recently just bough an Akai lpd8 for using as a basic midi control device to trigger the backing tracks and control volume.

The problem is that since the MacBook only has two USB ports, I am having to use a USB hub. However, when I use the hub and trigger my backing track in playback, it seems that playback freezes, not mainstage, just playback. I do have an on screen wave and the wave will play for about a second and stop. When I pull up the playback plugin, the play button is lit up as if the track was playing, but there is no audio and the wave file is stopped at about one second. When I try to click the play button to stop the 'playback', nothing happens. When I quit Mainstage and unplug the USB hub and only using either both interfaces, or one interface and the midi controller, it works fine.

I have tried to troubleshoot this issue but have not been able to figure it out. If anyone has any suggestions, I would be more than willing to try them out. I am trying to fix this by April 24 2013 as my band is entered in a competition and I would like to be able to put on a solid performance using the equipment I have.

ps. Irony - If we win this competition, I will be using the money to buy a new and more suitable interface!

Thank you!!