I have rebuilt the K3B 1.0.5 RPM packages from RHEL6 enabling libmad (mpeg audio decoding) and libmp3lame (MP3 encoding) support and adding a bugfix from the Fedora 12 K3B package, that fixes DVD to AVI/MP4 ripping support with 'transcode'.

The packages are in the linuxtech-backports repo as they replace the K3B distro packages.

These K3B packages still have one known bug for which I wasn't able to find a patch:
the progress bar when ripping a DVD with transcode does not move, it stays at 0% until the transcode is complete, but the transcoding works fine, so it's only a cosmetic issue.

Quick install instructions:
install the linuxtech.repo config file if you don't have it already:
su - root
cd /etc/yum.repos.d/
wget http://pkgrepo.linuxtech.net/el6/release/linuxtech.repo
install K3B:
yum --enablerepo=linuxtech-backports install k3b

The installation will also install two dependencies from the linuxtech-release repo (if not already installed):
libmad
libmp3lame