I have a Mac, but I am not using the CC softwares. I do not have a CC Libraries account, just an Adobestock account.
Many of the vector images I want purchase can't be downloaded or opened by my CS6 software. I am well aware of the migration to CC technology but is there any flexibility in the image being available to older versions of the Adobe software and also without a CC Libraries account?
There is no subscription needed to have access to Creative Cloud Libraries. Libraries are integrated with Adobe Stock subscription. Regarding use of images with CS6, do you receive an error when attempting to open these files in CS6 Illustrator?
You may want to consider upgrading to a Creative Cloud subscription, you can run the apps on both Mac and Windows machines, you'll have 20 GB of space on the Creative Cloud, you'll have immediate access to upgrades, which is great if you plan on upgrading your computer, because eventually CS6 won't run on newer systems, and your Creative Cloud Libraries will be accessible from your Creative Cloud Apps. You'll also have access to Typekit fonts.
I know, you may not be ready for an upgrade right now however, sooner or later it will be necessary. Keep in mind you don't have to subscribe to all of the Creative Cloud Apps, you can purchase individual subscriptions but the All Apps subscription is a better deal if you use more than one application on a regular basis.
Please let me know what issues you are having with CS6 and the vector images and I'll do my best to assist you.