This may help:
http://www.dimdim.gr/2014/12/the-rasber ... rough-i2s/
Is this is your DAC (your link doesn't work):
http://www.ebay.co.uk/itm/Audiophonics- ... SwEzxYPonx
I believe these are the connections you need to make:
from DAC to Pi GPIO;
5V to pin2
PWR GND to pin6 (gnd)
BCK to pin12
MCLK unconnected, as your DAC should have it's own clock
LRCK to pin35
GND dac to pin39
DATA to pin40
Then enable hifiberry DAC in your config.txt file.