I can use both mpd and shairport with my hifiberry DAC, as long as I don't have them running simultaneously.
If I try to start playing something with shairport while mpd is playing, then shairport shuts down with the message
FATAL: Alsa initialization failed: unable to open pcm device: Device or resource busy
It seems they can't share the device. I'm not an expert on ALSO configuration, but I've read that you can create a soft device that supports multiple sources and forwards the audio to a hardware device. So I set it up like this in /etc/asound.conf
When I try to use shairport with this device it shuts down with the following message:
ALSA lib pcm_direct.c:877:(snd1_pcm_direct_initialize_slave) slave plugin does not support mmap interleaved or mmap noninterleaved access
ALSA lib pcm_dmix.c:1030:(snd_pcm_dmix_open) unable to initialize slave
FATAL: Alsa initialization failed: unable to open pcm device: Invalid argument
Does anybody have any experience of running mpd and shairport together with hifiberry? How did you configure your devices?