Richard
I'm fairly sure that the LJ M475dn supports downloadable PCL5bitmap soft fonts, of formats 0 (bitmap (deprecated)) and 20 (resolution-specified bitmap), and also the scalable format 15 (TrueType) and 16 (Universal) ones; not sure about the old format 10 and 11 (Intellifont scalable) types.
I have in the back of my mind that there is a slight problem with downloaded soft fonts on this (and simlar?) models: downloaded fonts, even if set as 'permanent', do not persist once the printer enters 'sleep' mode.
If i get time in the next few days, I'll try to confirm the above.
Chris