Chaley, thanks
I was trying to be a bit lazy I think and didn't really appreciate what CC actually did.
My books are epubs, but I think that doing it properly as you suggest will be a better option long term and so that's what I'll do when I get the time. Even if I don't get round to it, the ability to wirelessly connect my device with Calibre will be useful in the future and worth the money I paid.
Thanks again to you (and jackie_w) for the responses. I appreciate it.