So, we now have an iRex DR800SG in-house. However as far as we can tell the EPUB handling of images in the current firmware is horrific. HTML looks fine, PNG looks fine, but put those 2 in an EPUB container and it all goes badly.
Forum posts seem to indicate that the new firmware(coming soon...) will fix this issue. So we've suspended development on the DR800SG specific formats for now.
On the other hand, PDF formatted with 'Maximum Crop' Looks fine, if a bit smaller than the EPUB will be due to the reformatting we do on the EPUB(which is the main reason we generate them, that and EPUB seems to render faster on most devices)