Your reference to "the Tonys forum" rings a bell with me.
Although ATC is definitely the first full fledged message board I ever joined as a member, I do vaguely recall posting comments on a couple of theatre-related websites prior to 1997, namely the Tonys Forum and the original castalbums.org.
When the first volume of Isabelle Stevenson's The Tony Award book came out, I was so disturbed by the dozens of errors I noticed that I began posting comments on the Tonys Forum website hoping to get the errors corrected. It was very frustrating because its moderator didn't take any of my posts seriously despite attempts on my part to provide them with extensive documentation.
I also remember posting comments on castalbums.org, back when the moderator was Mike DiBenedetto. This was in the mid-90's. I had an e-mail relationship with Ken Mandlebaum at the time. Occasionally Ken would give me some bits of information about some obscure Broadway cast recordings. So I began funneling that info to Mike on the castalbums.org website. I believe Mike DiBenedetto was also a poster on ATC decades ago. Does anyone here remember him or know if he is still around?