2006-2007 Navigation disc on 2003 unit?

[Witchfinder]

I've been looking at updated navigation discs on Ebay, and they look much more reasonable than the £270 the dealer wants. However, some of the auctions mention that the update disc only works on 2005-2007 cars, and not on the earlier Denso naviagation units. I have a 2004/53 plate ST220, and I checked the "secret menu" detailed on http://solesz.extra.hu/ and it looks like I have the older unit (part number 3S7T-10E887-AE). So I assume I have the one of the older units.

If the new discs don't work on the old system, what are my options for upgrading the maps?

EDIT: Just a quick note as a word of warning - if you use the "secret menu", you can theoretically trash your navigation system.

Edited by Witchfinder on Saturday 15th December 20:00