Angel,
It is not clear from you answer whether the 3 domains are subdomains of the same main domain or separate main domains. E.g. sub1.domain.com, sub2.domain.com & sub2.domain.com or www.domain1.com, www.domain2.com & www.domain3.com.
The difference is important as Pound can handle HTTPS connections for wildcard SSL certificates (*.domain.com). While C.R. is correct in that HTTPS doesn't allow virtual hosting, Pound can setup the SSL connection w/ the client and forward the request as a HTTP request to the backend server. Pound can only do that for 1 wildcard certificate.
I've made some modifications to OpenACS (not yet committed to CVS) that allow OpenACS to handle the proxied HTTPS requests (which OpenACS receives as HTTP requests w/ an additional HTTP header indicating that Pound received the requests as HTTPS) as if they are secure.
/Bart