As per your membership, you can download all JATC extension that comes with template package.
You can download all extensions from the template page, not from JAEC section.
JAEC section needs JAEC membership.
You have access for all JATC extension as mentioned on the pricing page.
if you want to download JA Masshead module you can download it from the template packages that comes with this module.
Some of the extension are not in JATC section like JA K2 filter as they need a separate membership.
Let me know if you will want to transfer your JATC membership in JAEC, I will share your request to the sales team.