I had a bunch of pictures of the Macs powering all the displays on the set of the NX-01 on a hard drive somewhere. I should go see if I can find them and post them.
Here is Denise Okuda in front of her Quadra 700. She used it to make all the wonderful LCARS and other alien UI panels on DS9. This was her taking a break while working on the DS9 pilot in 1993.
They needed something that was just going to put a fake computer display on the screen and they went with Mac's? That's not... Exactly a cost-efficient way of handling that. Then again maybe they had some kind of weird corporate thing going on?
my guess would be it was the smallest/fastest mac they could get and the scenic design team used macs almost exclusively and probably had no interest taking a chance on a different platform. Just a hunch tho.