If I remember correctly, both Dell and Rio have the same hardware. The Dell ones came with an updated firmware (1.04 vs 1.03), but this is only revelant if you use the included software. In fact, I think I remember that it only add support for Dell units to the server, no new functionnality. I own a mix of both (2 Rio and 2 Dell) and they're working happily together.

Currently, I'm using medianet. It has many functionalities not found on the original software. The best ones are: The possibility to append/insert to current playlist; The original software can't do that. Also, it support transcoding to mp3 to play different kind of audio files. It also support shoutcast streams. Finally, you can sync many Receivers together to make them play the same thing in different rooms. Ah, and there's also the web interface. The screen is so small on the receiver, it's sometime difficult to see what's going on. With the web interface, it's easier to choose music.

An other alternative you have is trio . It has almost the same functionalities than medianet, but is java-based. It means that it's not easy to start as a service in windows. medianet is a service so you don't need to start it and you don't see that it's running. With trio, you see a cmd prompt window, or you have to use something like firedaemon to make it a service.

Of course, you have to manually edit configuration files to make both of them to work. The original software did work as-is. It' just that it's quite limited. It does what's written on the Receiver's box, nothing more. Alternate software are better, but need tweaking.

If you ever need help setting any of those, I'd be glad to help.