Hard to say since you didn’t give us a link or model # for your Sony, but it sounds like you picked up a so-called “home theater in a box” (HTIB).
There are lots of problems with HTIB’s. For starters, since they’re cheap they don’t last long. Those proprietary speaker connections are another. Often HTIB’s come with speakers that have unusual nominal impedances, and since the amplifier is specifically designed to handle them, they don’t often don’t like other speakers with different impedances. Basically HTIB’s are stand-alone systems and don’t “play nice” with other equipment, either outboard hardware or speakers.
If you want to stick with the HTIB, I imagine your lack of surround (back speakers working) is merely a setting in the HTIB that you didn’t do correctly. Again, no way to advise further without a link to a manual that we can look at.
However, your desires for operating the outdoor speakers are beyond the capabilities of most HTIBs. If you’re serious about that you’re going to have to scratch the HTIB and start from scratch with a traditional AV receiver that has capabilities for a second zone (most do, even cheaper ones). You won’t be able to keep the Sony sub either, as it most likely is passive and as such works only with the Sony system. Another example of the general inflexibility of HTIBs.
Regards,
Wayne A. Pflughaupt