No search results for "6.1" or "7.1"?

I am trying to search the audio section for posts dealing with 6.1 and 7.1 audio. I have tried searching with single and double quotes as well as the + sign:
"6.1"
'6.1'
+6.1

Each of those search queries turns up no matches. I know there has to be quite a few posts referring to 6.1 or 7.1.

As a workaround I can search Google:
6.1 site:avsforum.com
But I'd rather use the AVS search links for searching specific areas or threads.

What am I doing wrong in my search query?

Thanks,
Tom

Ok, thanks for confirming that. I thought it may have something to do with the '.'

I can continue using Google to search avsforum, just a bit more digging around.

Thanks,
T