MythTV 0.25 came out just a few weeks ago and while my current 0.24/fixes systems are working just fine, 0.25 announced integration of Apple AirTunes/AirPlay (http://www.mythtv.org/wiki/AirTunes/AirPlay). While I'm not really interested in the AirPlay functionality that much, AirTunes is nice to get music playing in different areas of the house where my MythTV frontends already exist. I do own an AirPort Express that I have attached to the main stereo, but free software on Linux means I can increase the available speaker destinations to any location my frontends exist.
There's a Linux code project called Shairport (https://github.com/albertz/shairport) which makes this possible. It's nice and easy!
On Ubuntu, you need some supporting packages installed to compile/run. Do something similar for your flavor of Linux:
sudo apt-get install libao-dev libssl-dev libcrypt-openssl-rsa-perl libio-socket-inet6-perl
Then, get the Shairport code:
git clone https://github.com/albertz/shairport.git
Go into the ./shairport path and do a quick 'make'.
The resulting binaries are started with a little PERL and some switches. Mine wound up being the following, to run in the background and play audio from ALSA via HDMI:
perl shairport.pl --ao_driver alsa --ao_devicename "hw:0,3" --apname="MythTV LivingRoom" -d