Best answer by AjTrek1
First off I have zero knowledge regarding your Xnatech MRC88. What I can tell you is that in order to get your non-Sonos speakers to work with Sonos will require (a) Sonos Connect:AMP_using existing speaker wire or (b) Sonos Connect if they are powered with line-out. You can learn about the Connect Amp and the Connect respectively at links below:
* New verson of the Connect:AMP coming in February 2019.