im assumin the doors also close on the middle 'support'
If it was me i would cut it out and get some 3x2 or 4x2 and create a frame under the top so it carnt bend/bow down. I would also put a little door stop the bottom and top so when the doors shut they sit in the correct postions.
this is what i done when i modified a cabinet in my bedroom for my tank and sump.
Few pictures of the stand. (The H on the side is the top where the tank will sit on)
just brace it well 2x3 or 2x4 will be a whole lot stronger that what you have there, if you tank is full it will need to be removed before you do it but brace the insides on all 4 sides and and connect it and you wont need the center at all