It seems that jumping off the speaker wires can be do-able. I don't see any problems with that, unless you're trying to drive too many speakers throughout your entire house. And even so, you can probably wire it to the high level input of an amplifier.
As for extending the microphone, I think it may negatively affect your Echo. It seems to me that the 7 microphones are finely tuned so that the Echo knows in which direction you are speaking from. That is how it filters out background noises. Whenever you speak to Alexa, the blue ring on top lights up. The lighter/brighter portion of the blue ring indicate the direction you are speaking from. If there is background noise such as from a TV, Alexa can usually understand me if I stand still and speak. If I'm walking around the room and speak, Alexa will almost always fail in understanding what I said.