Hey audio gurus....

I just picked up a Kenwood 10" sub and amp package that I will be installing in the near future.
I'm not really sure how to run a pre-out to the new amp though....
Currently my Kenwood head unit has both of the front/rear amp pre-outs running to a JBL 4 channel amp and driving 6 DB651s....
There are no more pre-outs on the head unit, but the JBL amp has an unused aux pre-out. Could this be used to run the sub amp?
I read the JBL owners manual, it's useless and doesn't even refer to the connections....
I guess my only other option is to split one of the pre-outs at the head unit.
Just looking for the best way to get a signal to the sub amp.

Thanks,
BB