kyteflyer, thanks for your comments, but I think you are completely missing what I need :-)
What I want is to read and sync non-drm ebooks, i.e., third-party books I load myself. There are several solutions that support reading on the computer and syncing to an iOS app, including Kobo and Kindle, but only with drm books you bought from their store.
As far as I can tell, the new Sony iOS app doesn't even support that. I think it supports it on Android, not sure, but that doesn't help me... I hope it's something they'll add in the future.