Alpine PXA-H800, 2015 Nissan Rogue, Input for Subwoofers

Hey all. I am going to be adding an Alpine PXA-H800 DSP along with a Kenwood 4 channel and Sub amp. I will be retaining the factory radio and no longer using the factory bose amp in a 2015 Nissan Rogue. Right now the radio output's 4 channel's (plus the center channel). There is no sub output as the factory amplifier must have took the rear signal and split the output to the factory sub-woofers. I am wondering how to get the input for the subs. Can the PXA-H800 take 4 channels in and output 6 channels? (2 for the sub)? If that is not possible, is it silly to use the center channel output from the radio to feed channel 5 and 6 on the PXA-H800 for sub output? How would you guys go about a situation like this? Thanks! Justin

It appears I can input 4 channels and output 5. Unit is filled with features. Hope this goes well.