Install OSMC on Raspberry Pi headless?

Yes, just image the SD card as normal then boot from it on the Pi - wait at least 15 minutes so it has plenty of time to finish installing. You can pre-configure static IP’s if you like from the installer.

Do you have something against the OSMC installer ? I don’t know what Pi Filer is so can’t speak for whether it will write the image correctly. Another way that would probably work on Mac OS X (although I have not tried it) is to unzip the image (from .img.gz to .img) then use Disk Utility to write the image to disk.

A third option is to use dd from a command line but you must be very careful to identify the correct drive (using ‘diskutil list’) so that you don’t wipe your hard drive…

On the contrary, a fresh install does have SSH enabled, so if you are unable to log in via SSH then the install has failed.