I followed this thread to wire up some 6x9's I put behind the seats, thanks makeao for the info
As in other thread about adding speakers and it throwing off the staging, there's some truth to that. However, I overcame the problem by adding an equalizer app to my Nifty City table that had L-R balancing, and then I re-pinned the jumper harness so that the front speakers are on the Left channel, and the rear speakers are on the Right channel
Now, I can balance the front - rear staging perfectly