I connected my rear speakers to the converter and the front/rear speakers together. This is the only way to cintrol the sub output
OK I tapped into the rear speakers via the RCA converter and that's worked a charm so far. Tomorrow I'm on a mission to grab myself a decent switch to control the amp's power on/off. It was actually far easier than expected. I will update this post later on to better clarify the process for anyone else going through this.