While stumbling around the internet trying to find out how to retrieve the serial# of a locked MK2 navigation unit, I found this diagnostic manual for the MK3. The link works for now, but I've attached a PDF version for logged in users for posterity.
Covers all sorts of stuff apart from audio but it seems to be primarily for the North American version with XM, Lanewatch etc although 95% is common to UK/Euro units. I don't recommend messing with it unless necessary.
http://techinfo.honda.com/rjanisis/pubs/sm/1/2/Contents/enu/61TR0D/TRS/SCT/SC/SYS/T001200_enu/web/html/T001200_enu.html--
TG
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