You don't need to use Calibre to transfer mp3s to your Sony (actually, I'm not sure it would work if you did).
You can just do it manually: create a folder somewhere on your SD card, copy your folder full of mp3s over, and then the Sony should automagically spot and load them into the Audio section.
I just tested it out on my own PRS-T1 and it worked okay (the volume on the audiobooks was a bit low, even with the slider turned up, so you may want to try tweaking the volume/equalizer control on the files via iTunes or similar beforehand, though I don't know if the Sony would accept those new settings).
|