hi helen, and welcome to the forum ! i'm very glad to know you didn't have the same problem as i did, since you couldn't even *attempt* a repair at your local sony store (i'm sure they'll get there eventually. it took them a while to get to france, but they made it).
you're quite right that calibre is about a million times better than the sony software for managing your library. i use it exclusively, myself. i'm not sure it has an epub *validator* though ; although that might be a new feature that i haven't noticed yet. but if you are looking for more than a basic converter, you might try sigil (it has its own forum here) for editing and creating epubs, and the
threepress.org validator.
enjoy your sony ! and happy reading.

i recently re-read the HHGG and it's definitely worth it, although i still think my favourite douglas adams books are the Dirk Gently ones (alas, there are only 2 of those.

).