I apologize if this has been answered anywhere already. I did not find this answer for that matter even through searching the forums. Either it was people getting directed to the FAQ , which actually did not answer this or the support which had about the same merit.

So my question is:

I have the base game of ESO. Playing since day 1 so my game is not on steam and the only thing we DO know is that the non-steam game can not be linked to steam.

So far so good.

I only find steam products on amazon and other sites for the digital upgrade however. Can I pre-order this and use it on my base ESO without having to buy the base game again on steam?