Hi Tim,
We do plan to eventually include audio export options, but your choir members probably want audio
now 
One way you can do it is to use SynthFont (donation-ware currently 15 euros,
www.synthfont.com) and use the "Play to file" option. This renders the .mid file to an audio file (you can render to a variety of audio formats) that you can burn to CD or use on mp3 players.
SynthFont is also nice in that you can use soundfonts with it to get better sound for your members. It will use the GS Wavetable by default (just like Composer) if you don't have any soundfonts available. But there are a lot of free ones that are really nice (check our page at
http://www.notation.com/Articles-Soundfonts.htm for sources). Almost all the General MIDI (GM) soundfonts that I've found sound better than the GS Wavetable.
If you want to use these same sounds while using Composer, you can install a virtual MIDI cable to connect Composer to SynthFont. I use LoopBe1 (free at
http://www.nerds.de/en/download.html).
1. Install LoopBe1,
2. run SynthFont,
3. then run Composer.
4. In Composer, select LoopBe1 as your playback device.
5. In SynthFont, click the "Activate Midi Input" button.
Now you'll hear the soundfont sounds when you use Composer
Enjoy
Sherry