the speakers suck. Like some girls I dated in the past, pretty, but useless. You really can't use "real" speakers with the main unit and the specs are so overrated as to be a joke.
And, I could be wrong, but it looks like the woofer is he brains of the unit and contains all the major electronics. And, since all speakers are driven off that sub, that makes it impossible to upgrade or substitute. Likewise, that central unit is worthless without that sub and speakers. IOW, what you've got is what you get ...forever.
Personally, I'd take that money you have earmarked for this white elephant and repair or replace your "real" receiver and keep your existing speakers.
But, it seems you've got your mind made up. Enjoy, but don't come here expecting for any advice as to make it sound better. It can't be done.