1.04 software is supposed to be functionally identical to the 1.03 software ...

Right. Time to clear this one up once and for all. I did a diff of the source code between the 1.03 and 1.04 releases. I found:

• numerous changes to the .dsp and Makefiles -- none of which appear to affect functionality/bugs
• Global volume control (me -- Ibiza)
• Better escaping of characters in HTTP requests.
• Sorting support in the list of units in Receiver Manager (me -- Ibiza)
• Minor changes to the tracing.
• Support for rebadged Dell units.
• A couple of (minor) fixes to pause/play behaviour on the unit.
• Better support for servers that don't support saving "favourite" playlists.
• Changes to the version number and copyright years.
  

So, none of the changes between v1.03 and v1.04 will have affected the ability of a (non-rebadged-Dell) unit to boot.

Why v1.04 isn't on the FTP site, I don't know.