I also tried removing the entries in /etc/asoundrc.conf (since I found one old? page on your site which didn't mention these changes). The result was that sound was playing but was interrupted/distorted every few seconds.
Otherwise I always get the "Device or resource busy" error message
I was previously using the built-in sound but removed that module from /etc/modules
I have previously installed audio-related gmediastreamer (for DLNA player) and bluetooth but have tried stopping/disabling these services without any change in audio output.
pi@rpi-kitchen ~ $ ./check-system.dac
Linux rpi-kitchen 3.12.28+ #709 PREEMPT Mon Sep 8 15:28:00 BST 2014 armv6l GNU/Linux
PRETTY_NAME="Raspbian GNU/Linux 7 (wheezy)"
snd_soc_bcm2708_i2s missing in /etc/modules
bcm2708_dmaengine module not loaded
module file /lib/modules/3.12.28+/kernel/drivers/dma/bcm2708-dmaengine.ko not found
**** List of PLAYBACK Hardware Devices ****
card 0: sndrpihifiberry [snd_rpi_hifiberry_dac], device 0: HifiBerry DAC HiFi pcm5102a-hifi-0 
Subdevice #0: subdevice #0
aplay: main:682: audio open error: Device or resource busy
pi@rpi-kitchen ~ $ dmesg | grep dmaengine
[ 1.338180] bcm2708-dmaengine bcm2708-dmaengine: Load BCM2835 DMA engine driver
Thanks for helping