Well, looks like you've had a go with xPLRioNet before...but as of the v3.8i (21-Oct-04) version, it has the following:
  • Support for Rio, ExStreamer, SliMP3, MVP and WinAmp.
  • Multi Unit MVP support.
  • Built-in customizable web interface.
  • Support for MP3, WMA, WAV, FLAC and OGG.
  • Support for synchronizing multiple Rio's
  • Shoutcast support (including support for DabBar/Wavefinder MP2 streams)
  • Text-to-speech announcements (via xPL messages)
  • On-screen messages (via xPL messages) e.g. for caller ID etc.
  • Generates Pronto/Pronto Pro csf files (for quick album/artist/playlist selection)
  • Generates Voice Recognition files (for use with xPLRioNetTTS and xPL_Voice)
  • Uses any ODBC-compliant database (ships with a Microsoft Access database)
  • Can be fully controlled and monitored using xPL messages
  • Installs as a Windows service using Microsoft .NET technologies

I realize it is not Linux based, but... there are some efforts of developing Linux applications of the xPL platform, perhaps xPLRioNet will come along there too...?!?

Given the feature set of this latest version, I'm pretty excited about rolling this out at home--including synching players.

I'd say consider it again...

Cheers,
Tim