Edit:
Sorry just reread your post! 
Ques 1/ Can you confirm that your goal here is to output the Amp audio to your TV Arc?
I would suggest that the Source is the input and the Display is the output. If that is the case and the answer to Ques 1 is Yes, then the Source would connect to the Amp and the Display/Output would connect to the TV Arc input.
I don’t think this will work, but I’ve never heard of a unidirectional HDMI cable.
ARC passes data both ways: audio goes from the TV to the audio device, but CEC goes both ways as a part of the connection/codec negotiations. ARC can’t work without CEC. (Now eARC CAN theoretcially work without CEC if the Ethernet-over-hdmi is supported by both ends and the cable, but again that is bidirectional).
I would certainly test this cable with the devices in a pile on the floor next to each other before wiring it into a wall.
Edit:
Sorry just reread your post!
Ques 1/ Can you confirm that your goal here is to output the Amp audio to your TV Arc?
I would suggest that the Source is the input and the Display is the output. If that is the case and the answer to Ques 1 is Yes, then the Source would connect to the Amp and the Display/Output would connect to the TV Arc input.
My goal is to connect a Roku to an outdoor TV via HDMI, run an HDMI cable from TV outside to Sonos Amp inside to be able to pass the audio back from the TV/Roku to the Sonos Amp and listen to the TV over my outdoor speakings in the ceiling of my covered patio. The reason I am using a directional / fiber optic HDMI is bc the run is prob 50-75 feet and a standard HDMI isn’t great at handling that distance
I don’t think this will work, but I’ve never heard of a unidirectional HDMI cable.
ARC passes data both ways: audio goes from the TV to the audio device, but CEC goes both ways as a part of the connection/codec negotiations. ARC can’t work without CEC. (Now eARC CAN theoretcially work without CEC if the Ethernet-over-hdmi is supported by both ends and the cable, but again that is bidirectional).
I would certainly test this cable with the devices in a pile on the floor next to each other before wiring it into a wall.
I unfortunately can’t test this as everything is being built at the moment and I don’t have the Sonos Amp or the speakers. I suppose I can waste some $ and have the installer run two of these cables, one in each direction so it’s foolproof.
For reference, this is the cable I purchased and intended to use: https://www.amazon.com/dp/B09ZXQJHYN/ref=dp_iou_view_item?ie=UTF8&psc=1
My other option would be to use an HDMI Balun and send the ARC over Ethernet / Cat6 but I was trying to avoid introducing another fail point into the equation
Ok so maybe back to square 1 which is what my original idea was. Something like this: https://www.amazon.com/dp/B07HH1212W?ref_=cm_sw_r_apin_dp_ZWA4P5K5C992YPV102VS_3
And if I do end up using an HDBaseT to send the audio signal back will I be able to control the Roku / TV volume using the Roku remote and it will send the volume control back to the amp to increase / lower the volume?
I’ve seen this solution but don’t have access to purchase as I am not a dealer: https://www.snapav.com/shop/en/snapav/binary-audio-return-extender-for-hdmi-arc-and-spdif-b-260-arc-a
The unit that you found on Amazon should work. Full disclosure: I have no experience with this type of unit.
HDMI-ARC over CAT-6 is a relatively new development. At this point very few devices support this.
