I have implemented Sigma (paid for pro) and it seems to be working very well.
Just an FYI: your redirect script adds variables (height and width) to the chat.php script. If a site (like ours) has SIGMA restricted to launch from one page ONLY, (i.e.
http://www.babynames.com/boards/chat.php ) it will fail if it is launched from chat.php?width=750&height=400. So I had to disable the redirect portion (screen options).
Here is a screenshot of our working SIGMA PRO chat:
Thank you!!!