hellow everyone i am new here.
i ran into some problem, trying to figure out if it can be done with some kinda of mixer or converter, please help.

here is my current set up on my car
1 x Head unit out to 1 x 2 channel Amp for door speakers , and 1 x mono amp to 1x sub in my trunk.

so i was wondering if i am going to add a tablet mount to my car as a Navigation and Torque app {not playing musics}.and using the existing amp set up what will i need if i want to play music from my current headunit n can be able to lisen to the tablet from the same speakers?

i don't need to wire the tablet to my sub ,since i am not going to play any music from my Tablet, just Navigation , so i will need to wire to the speaker ,since i need to lisend to the road instructions.

i am thinking maybe, i can just go n split the 2 channel speaker RCA wire input from headunit to 2 x input -> 1 x input to my amp, and live with it?
will that work? but i don't want to lose the current sound quality while playing music.
or i wll need somekinda mixer or anything
help plz.
sorry for my bad English/