dude since youve been waiting so long I'll try to help (I'm sure you're wanting to get moving on your new system. I have PT 7. Hopefully not much has changed, but anyway, on the top of the screen you will see either window or view (can't remember the exact button), let the options drop down and click mix. It is that easy on PT 7, but I suppose it may have changed on 8.
Luck
James