I have a whole-house audio system by HTD and I want to do this exact thing. I am thinking of just splicing the speaker wire, putting in a toggle switch and a headphone jack. I was hoping someone else (braver than I) would confirm this approach... but I might just rip it apart and try myself. My HTD system actually has stereo input jacks in each room (built into the panels) and all I'd need to do is plug the output from alexa into one of the rooms, and then use the intercom to talk back to that room... presto, now Echo would be reachable from all rooms.
Curious to know what your thoughts are related to being able to add a headphone jack to the echo. Normally, I'd just think about splicing the speaker wires and putting a switch in the middle so I could toggle between the headphone jack output and the onboard speaker, but it appears from the photo that the speaker is connected using a ribbon cable? Can you confirm?
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