Ugh...I hate a puzzle...
OK...I installed Calibre 3.0 and set up a content server. I was able to get it to work just fine using the read/download functions in the browser. I was also able to get it to download just fine using Marvin 3.
Although, there was a learning curve there. I had to select the correct library and make sure the book I was trying to download into Marvin was - in fact - an ePub, and not an AZW3 or Mobi. I will have to do some more research into setting up the Content Server to do that function automatically....tomorrow.
Good news: It's not a Marvin OR a Calibre problem. It's a user learning the new software issue.
Cheers,