On the assumption that the existing platform is, for cost (or lack thereof) reasons, the default, then if there is no satisfactory calendar capability and/or no volunteer who wants to wade through mountains of spam, then a link or sticky to the other site may be our best option. I'd suggest removing at least the "Event Calendar" sticky in the Event forum, as it is very out of date...
If you want to take this esoteric discussion offline, PM me and I'll give you an email contact - David probably already has it...
S.