Just a few things.
Your receiver isn't a multi-zone receiver from what I can tell. That means if you connect some speakers to the main outputs while connecting other speakers to the surround outputs, each will get different sounds. The music may be the same but the matrix surround processor added echo and phase changes to the channels to simulate surround sound. Have you thought about using a true whole house amp like
this? Or maybe use a 2 channel receiver/amp and an impedance matching distribution box like of of
these. You also have to make sure your volume control is compatible with the distribution method you choose. Some are more advanced and allow source selection and send a signal back to the amp to control the volume. Others are less complicated and use resistors or a transformer to control the volume. Parts Express and Smart Home have hundreds of components. Search for "Whole house audio" and it should return everything you need to complete your system.
Connecting multiple speakers to one set of outputs is not recommended unless you know what you are doing. I bet the volume controls are raising the impedance and preventing your new receiver from blowing up. You are lucky.
Your friend doesn't know what he is talking about. Don't take his audio advice.
You may have to purchase more equipment to get your system to run the way you want it to. Cobbled together systems will just frustrate you and the rest of the family. No one will use it and it will be money wasted.
Finally, why aren't you setting up your receiver with front speakers, etc. so you will get full surround sound?
-Robert