It would be a complex wiring diagram for a pre-amp line out. It would involve purchasing and developing a circuit for a DAC chip that supports I2S. Either that or a chip which can convert said input into SPDIF. The good news is the amplifier chip is also the DSP, so if you managed to pull and decode the I2S data you would have an unaltered digital audio signal. You might lose volume control unless you pulled that into your DAC as well. It would still be an interesting project if one had the time and money. Of course Sonos could just stop ripping people off with the Connect...