I think they are attached and are meant to be played like that because he says in his blurb.... "
with a modified front panel to accomodate the two X-Arcade controllers" . Looks like they would be easily detached though.
Either way it looks quite horrific. Even if he wanted to be lazy and still use the X-Arcade components, how hard would it be to take them apart and just pop the bits into the original panel? Or just nail some 3/4" wood across the the front and pop the controls right on top? Even that would be better.

Having said all that he probably just wants rid of the whole thing and if he did dismantle the controllers he cold lose some selling potential. He does say he has the original boxes for the controllers and I could see someone just wanting those.