You might want to try this suggestion which worked for me:

a: in a terminal, type "sudo chmod -s /usr/bin/xsane"
b: sudo edit /etc/sane.d/dll.conf, and comment out (add a "#") in front of the line that says "smfp" (probably the last line).
If you only do (a) and not (b), xsane will crash.

Though I do not have a multi-function printer, my scanner quit being detected when I installed the Samsung unified driver. My scanner is a Canon. When I followed the 2 steps noted above that another fine forum member suggested, my scanner became detected and commenting out the "smfp" that the unified printer driver had put in didn't affect how the printer works. Both now excellently. This might work for you but I'm no expert.