Those speakers would almost definitely be underpowered and much more likely be blown due to lack of power. The 15" subwoofer in that cabinet is designed, quite obviously, to be part of a soundstage setup, and not ideally setup for home theater use. Really, you want a separate, dedicated amplifier to handle the 15" sub contained within that box.
If there was no 15" speaker, than you would be in a much better postion to power those speakers, but the big speaker is killing you.
I wonder what would happen if you disconnected the 15" speaker from the rest of the speakers in the box though?
