Wire that "meets code" for in-wall use is often not audiophile quality. It depends whether the installation was a custom pro audio job or something the builder threw in to make the house more "modern". If it's the former, I don't think that a better wire from the jack to the speaker would make much of a difference for rear surrounds. Possibly, depending upon its sonic characteristics, it could be used to compensate for deficiencies in the in-wall wire though. But that's not "improving"; really, it would be more accurate to say that it is minimizing or countering deficiencies.
On the other hand, for the wire that's closest to the electronic components, a better wire would help. Cheaper wire may not be shielded very well and could pick up interference that may affect components. In that case, a better wire would help even though the in-wall wire it's connected to is not top quality.
Make sure you have good tight connectors.
On the other hand, for the wire that's closest to the electronic components, a better wire would help. Cheaper wire may not be shielded very well and could pick up interference that may affect components. In that case, a better wire would help even though the in-wall wire it's connected to is not top quality.
Make sure you have good tight connectors.