This is incorrect.
The *only* way to get the 5.1 version is in the Box Set.
The 2CD/DVD version contains 24/96 stereo (Original Mix Remastered & New Jakko Mix) only.
I'll be furious if this is true. I passed on the box set and pre ordered the 3 disc set (2 cd + 1 dvda), and, up to now, the descriptions of the 2 sets has always had the dvda in both sets as containing the 5.1 mix.
http://elp.merchnow.com/products/166324/brain-salad-surgery-40th-anniversary-cddvd