RPi B+ works with I2S DACs, if:
I did the patch (change three bytes in a kernel module) - works:
Raspberry Pi B+ and RPi-DAC
If DAC needs I2C for control - then it needs more effort to modify kernel (or wait for updated release,
even the most recent release June 2014 does not support yet).Without the Kernel Patch and trying to use I2S - RPi - the B+ will hang.