GSM and Nav system connection

I have the empeg working fine into 3 amps; 1 for the fronts, 1 for the rear fill and 1 for the sub. I have a speaking nav system and also a GSM phone car kit. I would like to feed the GSM and nav output to both channels of the front amp in parallel with the empeg.

So far I have put a potentiometer across the nav speaker level output with the slider connected to the signal line of the left speaker. This allows me to dial in the voltage to this channel and it all works well. The empeg hushes and the nav system can be heard above the music.

I would ideally like to output this signal (and the phone signal later) to BOTH channels but if I do this by linking the left and right input it works but obviously I loose the stereo signal from the empeg as both channels are bound together giving mono.

Question: What components would be required so that the Nav mono output can be fed into the 2 separate L-R channels without binding them together?

Is there any way to use one of those Sony XA39 switching relays in this setup? Then you wouldn't be combining channels at all.

My last resort is a home made varient of this, but was sure that someone with a good electronic engineering background here would be able to suggest a discreet component alternative.

If all else fails, I will have a relay 'bind' the 2 channels and the 2 external outputs when the mute signal goes low.

I was hoping to avoid relays due to the unpleasent clicking.

I was hoping to avoid relays due to the unpleasent clicking.

Not to mention the possibility of introducing noise and ground loops if it's a homemade system. I don't know if that Sony box "clicks" or not, but I'd lay you odds that it's less likely to induce noise than a homemade system.