Peter, I've tried the command line but can't seem to get it to do anything. I guess I really don't know what I'm doing.
At any rate, I also tried changing the ePUB association to Calibre by right clicking an ePUB file. I get an option to browse for the program I want to open. Among the program choices is Calibre2, but I don't know if that's what I should choose or if I need to look for something else? Thanks!