The benefit of the arc is pretty much lost I would say. I ordered a BenQ tk850 projector because said that it would support HDMI arc on one of its HDMI ports. However, I found out later that the projector could only output 2-channel stereo sound from HDMI arc. I don’t know if I am lucky or unlucky, but the projector I received has defections so I returned it without any problem.

I further researched into this issue and found that most projectors cannot output 5.1 sound even if they have HDMI arc. However, I think there is a HDFurry product (called arcana?) that can basically split your source input to send audio to sonos arc and video to your projector.