A tried this whole thing on my 60csx. I'm quite impressed with the result, it works fine. I can also switch between the database while searching. Cool. My only problem is the same. Custom POI icons doesn't seem to work. Actually, I managed to load the icons to the unit, but displaying is problematic. I loaded two different icons, but both of them are wrong. I only see the upper left corner of the image. Seems like the unit can only deal with a 4x4 pixels image, and cannot use any larger than the original blue square.
Looking forward for a firmware update, maybe it will help.