swapping internal sd card and usb otg
Since I've gotten a few hints out of this forum, I thought it'd be fair for me to actually register and contribute too!
I tried some USB OTG cables (amazingly hard to get - hardly anyone's heard of these things) plugged into the Vox and various USB things plugged in to them: keyboard, memory stick, camera. I also tried plugging in a powered hub. No go either way; I suspect a kernel module's missing.
I also swapped my internal SD card for a 32G one, and it's working fine - storage settings is showing that I have 27.66GB available space, yay! I dd'ed the original SD card's contents onto one plugged into the external slot (as luck would have it, the Sandisk 8G speed 4 card I had handy was a perfect match for what the Kobo has inside). Disassembled the Vox to swap in my copy and it booted just fine, so I bought a 32G speed 10 SD card and repeated the dd. On a netbook running Ubuntu Linux that has an SD card slot, I extended partition #4 to include the extra space. Disassembled my Vox yet again and popped it in... seems to work fine!