Yes, thanks for the tip about that plugin!
I also noticed they have a correction kit for monitors. That would be a cheaper way to tailor my speakers to my room peculiarities. But I've heard such solutions aren't very reliable. Likely to be better than an untreated room though.
Can someone tell me what it means by one instance and two instance? Does it mean I can only use the software once, for one room? Or does it mean on one computer?
While such plugins and programs don't fix all problems, they can help. I don't use it as a replacement, but as a supplement to room treatment. You need to treat first reflection points, and get at least SOME broadband absorbers in the corners. From that point, the software can help further.
Can you quote the section about one instance you mention?