You cannot increase the space available for expansion waves.
The best you can do is within YEM, go through those 10 packs and deselect any voices you do not really need to install. That will reduce the space they take up and give you a little more to play with.
Alternatively if you don't need them all at once, make up more than one install file and switch between them (i.e. replace one with another on the keyboard) when you need to. I'm not saying this is a great solution, but it might work for you.
But if you genuienly want all the voices in those 10 packs available at once, and more, then I'm afraid no matter how much you might want it to be different, you have hit the limit.