In order to get the extra stage(MaxX Unlimited) you need to AA your last song on Heavy.(it canot be on little).MaxX Unlimited will be on reverse,x1.5,dark,and on pressure mode.If you AA that song you will reach one more extra stage called Kakumei.

Another way of getting Kakumei is if you AAA your last song on Heavy.If you pass both extra stages you will unlock both songs!