>The main page MUST be named a ASP page for the SSI to work. rename the main page something like MyPage.asp instead of MyPage.html.

Ugh, no.
By default IIS is configured to process SSI directives in files that have stm, shtm and shtml extensions. ASP pages will also process SSI’s as well. You may configure IIS to process SSI’s in files with .htm and .html extensions as well.

I should add that configuring IIS to process SSI's on htm and html files will add another layer when processing the request. IIS will have to parse through the html page to look for any SSI commands. This would have a slight impact on performance and overall scalability.