Actually, the map isn't accurate; it's missing the Silver Line, which has been around a few years. Take the Green Line (I believe) to the Duck as I think you get it near North Station (?). I'm not sure but I see the Duck all the time when I've worked in the city -- hasn't seemed to matter where. Blue Man Group is in the Copley Area, I think (our theatre district, such as it is ), which would be the Green Line.
In case someone ever asks.
Thanks