I'm still using Studio 14 Ultimate HD (I know, but Studio 16 & up are not that user friendly to me) and I want to buy the Algorithmix audio plugin.  There are some sweet features that come with this, but being that I am using obsolete software, there isn't a way to purchase and install this.  Is there some way to get this plugin?  Any help is appreciated.  Thank you.

Not possible legaly to get it.

You're absolutely positive about that? It's strange, when I try to access it on Studio 12, it does go to the cart but then the final page doesn't load.    Another problem I have is that I bought a lot of downloadable add-ons over the years, but with different email accounts (didn't know that would be an issue at the time), so trying to get the ones I purchased back is next to impossible.

Absolutely positive.

If you did not make any backup of all this stuff, I'm afraid you won't be able to download it from Pinnacle's or Digital River's servers again

I wonder, do you know of any free plugins for 15 or earlier that can change the voice in the audio? Audio enhancer type of thing?

Not that I know.