Wiring question. Stock JBL speakers with 5 ch Amp

[acronin2]

I have a question for any audio gurus on the forum. I have an 04' sport that originally came with the JBL synthesis 10 speaker set up (no nav). I have replaced the head unit with with a 2013 Scion FRS BeSpoke touchscreen head unit and used the Metra TYTO-01 amp turn on module/harness. I've had this set up for about 2 months and have been very unhappy with the TYTO-01 performance. The sound cuts in and out. I have decided to go ahead and just replace the JBL amp with a 5 channel amp (Arc Audio xdi-805) and use the stock speakers for now. I am going to eliminate the center dash speaker up front and use the rest of the 9 speakers. My question is how to wire up the rear pillar speakers. I will be using ch1 for the front left, ch2 for front right, ch3 for rear left, ch4 for rear right and ch5 for the sub-woofer. I understand that the two rear pillar speakers use a mono connection. So how would I hook these up to the amp?? I am assuming I would wire them to ch3 or ch4 in series? But am a little confused on series vs parallel wiring and which would work best. Also not sure of stock speaker impedance. FYI i plan on using the Metra Turbowire harness 70-8117