So 10 seconds later I had a brainwave. You have to install MP drivers as wireless rather than USB. Then the IJ network scan utility installs and the scan buttons on the printer connect to the computer. Not sure why they don't work if you use USB thou...
This is driving me nuts. It used to work i.e. press the printer's scan button to save to PC but my HD recently failed and I've had to reinstall windows 10. MX876 connnected via USB. I've used the latest MP drivers, but IJ network scan apparently doe...