ReadyNAS Ultra 4 newly upgraded to 6.9.5 from OS4 and need question answered.

I apologize for posting a question I know has been answered in here, however I read the post about a month ago and I have been unsuccessful relocating the post for the past few days.

 

I recently upgraded my Ultra 4 from OS4 to OS6 and loaded all my data back onto it and everything is working great, thank you all for the many helpful threads here on that.  I have 4 x 3TB drives in it and I am looking to expand it, but I am unsure how big I can go from here.  Originally I was thinking I would be starting from the 4 x 1TB that I had initially, however I believe since I had to reset everything for the OS6 upgrade that I am starting from that point now instead.  So I'm thinking I still have my full 8TB expansion limit available?  So my question really is, what is the largest I can upgrade too from this point?

 

Thanks!