I hacked up a lua script to render Epson JX-80 output from the BBC Dumpmaster rom and it looks pretty good. It supports the JX-80 on printer number 22. 22 is color with square pixels, 0 is black and white, and 5 is 72x72 dpi for square pixels.
The luaprinter wouldn't work unless I set the acknowledge to 1 in device_reset with output_ack(1).
Doubling the dots horizontally on the printout makes it look vivid.
The output is stretched 200% using gimp to make the aspect look right and rotated 90 degrees to be upright.