All-in-one “home theater in a box” (HTIB) systems like your Sony are basically stand-alone systems that don’t accommodate “mixing and matching” with the products of other manufacturers. The speaker-impedance issue TLS mentioned is one problem. The other is that the connections used to connect the speakers to the amplifier are proprietary. So basically, if the electronics go out, you have to trash the entire thing, speakers and all, and get another one.
The “lesson learned” TLS mentioned is that bargain-basement HTIBs are notoriously unreliable and typically last only few years. A system like he mentioned with separate good-quality components will be more expensive initially, but will last infinitely longer. And if the electronics dofail, the speaker system can be re-used, so that expense doesn’t have to be repeated. On top of that, even the cheapest speakers will easily sound better than what came with your Sony.
An unfortunate side effect of a system of separate components, however, is that set up is more complicated.
Regards,
Wayne A. Pflughaupt