Alien Bob has a good number of 64-bit packages in his repository
and every one of them has worked flawlessly on my 2 Slack-x86_64
systems. He also includes the source and SlackBuilds in his repo.
He has libdvdcss-1.2.10-x86_64-1alien, 64-bit libdvdcss; and also
VLC and MPlayer in 64-bit.
If you have a problem with any of his pkgs/scripts, just email him
and he will help you fix the problem.
On my two 64-bit systems I'm not missing any apps from 32-bit.
As a caveat, I do have 32-bit compatible libs installed so that I
can run wine, and a couple of 32-bit apps such as Skype.
He also has a toolkit
to help you setup a SlackBuild and slack-desc
so that you can build Slack packages yourself. Check it out.