Do you know which sound system you currently have installed?

There's two main parts to the audio system, the "Integrated audio module" and "Amplifier-power". The audio module does all the input selection etc, and the amp drives the speakers. The two are connected via the MOST bus so you can't tap into the incoming signal to the amp from the audio module without some specialist (expensive) gadgetry.

From the wiring diagram there's isn't that much difference between the 10,12 & 15 speaker systems. In the 12 & 15 speaker system there are two subs fitted, but none for the 10 speaker setup. The only difference I can see between the 10 & 12 speaker setup are those subs. However but its not clear whether the amp model itself varies between the with-sub and without-sub versions, so there is a chance that amp could support driving a sub, it just isn't connected. It might be worth trying to see if you can get a sub output from the installed module before trying to find a way to tap into the outputs to another speaker. If the amp did support a sub I'm not sure whether you would need to change the configuration of the amp or not to make it do that.

 

Currently I have it connected to the front speakers.

Have to do some tuning because my acubass settings might be off which I didn’t set up yet. Basically on low volume I can’t hear my subwoofer but at higher volume the bass just starts increasing rapidly without adjusting any knobs for a couple of seconds.

With regards to the wiring diagrams I think the wire colours are different per amp setup so always check the wiring diagram and work off of those when doing your wiring for your system.