====================== APT sources.list =================== ZZz2wrJ1
deb http://ftp.debian.org/debian jessie main contrib non-free
deb http://ftp.debian.org/debian/ jessie-updates main contrib non-free
deb http://security.debian.org/ jessie/updates main contrib non-free
deb http://apt.osmc.tv jessie main
deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free
deb http://archive.raspbian.org/raspbian jessie main contrib non-free
deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free
deb http://archive.raspbian.org/raspbian jessie main contrib non-free
deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free
deb http://archive.raspbian.org/raspbian jessie main contrib non-free
---------------------- APT sources.list END --------------- ZZz2wrJ1
Why have you added raspbian sources on a Pi 3 ? This will cause you major problems.
OSMC on a Pi 2/3 is based on Debian sources (armv7 binaries) not Raspbian sources. (armv6 binaries)
Please remove these lines and put your sources.list back to how it originally was then try running sudo apt-get clean then try updating again.
Have you made any other changes to the APT configuration files/preferences on your system such as pinning ?
Edit: what have you added in /etc/apt/preferences.d/jessie.pref ?