Pro Tools Aggregate I/O

[gpcovers]

Hey guys I'm new to this forum and couldn't find the way to start a new thread cause I dont know if people still reads this one, I'm having trouble creating an agregate device on my mac, I have an M-audio Fast track pro and a yamaha mg-166cxUSB mixer, and I would like to get the ins from the mixer and from the ftp all at once, but it doesnt seem to work, I cant even create an agregate with the inputs and the outputs of the mg166.
I'm able to create the aggegate with the mixer and the ftp, then I go to playback engine into pro tools 10 and select this aggregate device, but I heard I have to do something in the I/O section and I couldn'f figure out whats that, I just clicked default on both the ins and the outputs but it doesn't work.. does anybody know whats the problem here? thank you!