I am wondering if TiVo is a "sole source provider" for the Western Digital My Book DVR Expander. I just spent close to $1000 for my TiVo Roamio and lifetime service so I was looking for a way to save a few bucks on the external hard drive. I bought one on Amazon that said it was TiVo compatible, but when I tried to install it, the screen said it was not supported by TiVo. I returned it, but I am looking for one that will work without having to pay $200 for it. Any suggestions?