I was just wondering if you could run a signal from
the stock amp to a second amp that would power
another set of subs. Next question is, if you do this
can you control the second amp and subs with the
subwoofer control on the stock head unit. Any replies would be greatly appreciated.
Thank you very much

I should have said "How do you run signal to the second amp from the stock amp so I can control it with the head unit". any help with this would be greatly appreciated
Thank you :?

There is no "line out" type of connection coming off the stock amp.

However, some amps will accept line level inputs (speaker wire) so you could connect the subwoofer speaker leads to an amplifier that would in turn control a set of subs.

Since the stock speaker leads are controlled by the subwoofer gain function on the head unit, turning the subwoofer gain function up or down actually increases and decreases the line signal voltage level - this is what makes the bass louder or softer.

So, snip the wires going to the sub, extend them to an amp that accepts line level inputs, and then run speaker wire from the sub amp to the new sub. Your other speakers will still be powered from the factory amp and you will still have sub control.