I have sold my Rio Receiver and am now using a Squeezebox player. The Rio Receiver was a great product, and had lots of fun potential, but if you want something open source with a better display, try a squeezebox.
This page describes an update of rioserve_0_20b.tgz from http://mock.com/receiver/server and I have sent the updates to Jeff Mock. Others have developed updates as well; my guess is that Jeff is not actively developing the software anymore. I've put the update here to share my changes with others.
if you are looking for a simpler set of perl code, without any web interface, try YARRS by Paul J. Lucas, which was based on Jeff's code and my (somewhat minor) updates.
Here is the README, with updated installation instructions.
In addition to this software, I recommend the volume knob
adjustment kernel replacement available from http://www.mock.com/receiver/audio/.
It's just a replacement for the
/tftpboot/192.168.0.6/zImage file (where
192.168.0.6 is the IP address of your Rio Receiver).
Use gunzip to decompress the zImage.gz file and replace the
zImage file from
with the new file.