Thanks for the tip, weldeyes!
Even though I couldn't install the iscan rpms, because they currently state that Sane ver. 1.03 is required (which I couldn't find anywhere on the Sane project page - I guess they're using the most current snapshot of Sane).
I solved this with my Stylus SX415
by uninstalling the printer in PCC and installing it directly from within the Cups web utility to get rid of the error "PID xxxx (/usr/lib/cups/filter/pstoraster) crashed on signal 13!"
I also had to blacklist the module usblp
and restart the Cups server because of the error "usb 1-4.3: usbfs: interface 1 claimed by usblp while 'usb' sets config #1"
Now that printing worked, I set up scanning by using sane-find-scanner
and then scanimage -L
Because of your tips I was shoved in the right direction, so now everything works just fine. Thanks again, weldeyes!