I am using my Raspberry Pi 2 as a network player/transport for OpenHome, UPnP-AV, and AirPlay. It outputs an I2S signal to my external LKS Audio MH-DA003 DAC. It has no analog audio output by itself.
In order to improve jitter of the I2S cock signals, I attached a HifiBerry DIGI+ to the I2S bus as a bus controller providing the clock signals. There is no change required to any drivers, because the DIGI+ is a receiving I2S bus master and bus controller at the same time. You can also use the DIGI+ S/PDIF and the external DAC at the same time.
By request from other threads, here are some pictures of my setup and pin out. Please be aware that there is no standard on I2S over twisted pair cable and pin assignment on the RJ45 jack is proprietary and differs from vendor to vendor. This setup and pin assignment works for a LKS Audio MH-DA003.