I might mention that before going the Iancanada route I wanted to try the Magna Mano Ultra mk3 Farad network bridge that has both I2S and sp/dif outputs. It seems to be a very good unit (with a fine power supply) that doesn't break the bank. The problem for me was that the I2S output on the Magna requires an HDMI cable with the PS Audio pin-outs and the 005 requires the Gustard pin-outs. I looked far and wide for someone to make up a cable going from one to the other and came up empty. Since the 006 has pin-out options you also have more options.
As I understand it, the sp/dif standard takes the 4 signals from the raspberry pi (or other similar mini-computer within the device-often a raspberry pi) and combines them into the one sp/dif signal. Then the DAC internally separates them back to I2S within. Thus I2S direct avoids these two conversions. There are those who hear no difference; there are those who do.