Hi madwac!
Rhythmbox is a great player. The problem here is not the player itself, but the mp3 format. As you know, mp3-format is a patented format. Mixing things completely free(as Linux) with things that are not (like mp3 and codecs) are usually a problem. MP3 has been removed from Redhat since 8.0 if my memory serves me right.
However, you as an end-user should care more how to actually have mp3 support on your distribution right
. Check the FedoraFAQ:
http://www.fedorafaq.org/
The "How do I play MP3s in Fedora?" is the part you might want to look first. I am not sure if Rhythmbox plays midi files. It does not in my box. When I have to play a midi file in Linux, I use my own tool written in Java, jmidi, which you are welcome to use:
http://goto.glocalnet.net/torch/appl...midi/jmidi.jar
Usage: java -jar jmidi <filename.mid>
If you find a way to play midi in Rhythmbox, let me know.
Best Regards!