Hi Kovid,
Thanks ever so much for your reply.
You're right: I've checked the Calibre files with the ebook viewer and the Greek characters display properly on my computer screen. So really, it's matter of getting the Sony to perceive the file as a book, not a periodical, in order to give me the extra font options. I have now been able to do this
by saving the ePub file only (not the opf or the jpeg) onto the Reader; it's a tad fiddly because I have to manually copy the files after downloading them.
If I could change the default font from "original" to any of the other fonts that are available on the Sony and can handle Greek accented characters, I'd solve the issue, I guess. I'm going to search the forums and also Sony support to see if it can be done, and if so, I'll report back here.
Thanks again.