I'm probably going to lose a lot of geek-cred here, but if you're on hour 4 of wrestling with your SANE config, have some mercy on yourself and checkout vuescan. It works flawlessly on linux with every scanner I've tried: https://www.hamrick.com/
It's too bad people look at proprietary software with such disdain. Yeah, I'd love it too if all the world adhered to open source, but there are too many useful and awesome applications that simply aren't open source, where the open source "alternatives" pale in comparison.
As a supporter of free software, why should I advertise for the competition?