Steve,
I'm honestly not sure exactly what you're looking for. I've never used Ecwid before, but heard a lot of good things about it. However, I don't know it well enough to know it's SSO abilities (even reading the post you mentioned) or how it would work with Joomla login.. so, I may need some more info.
JFBConnect does create standard Joomla users. So, if you use the SSO solution with Ecwid, if it lets your Joomla users sign in to both, then JFBConnect *should* be able to do that too. I can't guarantee it (like I said, don't know exactly what I'm talking about). However, if the above isn't a good explanation, let me know a bit more about exactly how it should work, what is (or isn't) working now, and what would need to be changed in JFBConnect to make it work.
Thanks,
Alex