Why not simply turn-off the lightbox in the stack settings, using the checkbox option already provided? Then whatever URL you provide against an image in column #6 of the CSV file will get applied as your thumbnail link instead. ProGallery has supported this since version 2 and a lot of people use the stack like this.
If you did want to be talked-into going the CMS route, then my personal recommendation is that you take a closer look at WebYep. One of the stacks included is a responsive thumbnail grid. Images are automatically resized as you login and upload them. It is easy to reorder images in the grid and delete older ones. And like with ProGallery, the lightbox can be disabled, so you can apply regular URLs to the thumbnails instead.