The SD Card board probably has a 3.3v regulator on it. Bypass it as it will not function correctly when supplied with 3.3v only something above that like the Arduino's 5V. See this video I did showing the "bodge" I made when I came across this problem recently, the link takes you right to the correc...

Bit of a late reply but I've written a high level library for producing sound via the DAC. Key points : Samples can be any rate up to 44100Bps and the library will auto find this information from the sample supplied. Multiple samples can be played at once (the library will mix the waves together to ...