When we moved from 5.5 to 6.5, we created releases for our automations in 5.5 and imported them into 6.5. I would imagine you can do the same from 6.6 to 6.8.
On a related note, I hope you are doing thorough testing of 6.8 before migrating. We found dozens of issues with our migration, and the testing took several months. We found a lot of issues with BP 6.5 itself, from lack of work queue filtering to release imports that need to be done twice in order for them to work. You should test everything, every little thing, to ensure that 6.8 doesn't have issues before you migrate. BP does not provide a listing of bugs; you have to find them yourself and report them. Often, BP doesn't even know about an issue until you report it. In any event, BP doesn't patch existing versions and you have to live with some issues until you can upgrade to the version where they do fix the issues. In a large enterprise installation like my company has, upgrading (as I mentioned) involves months of testing, so we're finding we have to live with several issues potentially for years. Bottom line: BP appears to be seriously lacking in regression testing, so it's up to you to test.
Please do let us know how you fare with your upgrade.
