BTW, thanks for the teardown, otherwise I would not have attempted this and just sent the unit back for return.

Dave, just did this today. Spliced into the speaker wires (need to splice both tweeter and sub wires), to audio out jack. Now I can plug into house stereo which is the split throughout the house. Echo speakers continue to function as well. The most difficult part was mounting the audio out due to space. Ultimately just ran the spliced wires out of the echo and made a little audio out housing box which sits next to the echo. I have no plans to now move it since audio is now pushed through the entire house. The seperate audio out box does not bother me since it is hidden behind the house stereo.